U.S. President Barack Obama issued a cautious warning Friday that Syria's reported use of chemical weapons could be a "game changer" that could provoke international intervention in the country's ongoing civil war.

Both U.S. and Israeli intelligence claimed this week that Syrian armed forces have used chemical weapons in its battle against insurgent forces.

Obama had previously warned that chemical weapons represented a “red line” that could provoke a strong military response if crossed.

Although U.S. intelligence reports Syria may have crossed that line, Obama did not commit to any specific action.

"We have to act prudently," he said. "We have to make these assessments deliberately. But I think all of us ... recognize how we cannot stand by and permit the systematic use of weapons like chemical weapons on civilian populations."

Syrian officials denied using any chemical agents, saying it "did not and will not use chemical weapons even if it had them.”

Canada's Foreign Minister John Baird said Friday that he finds the U.S. and Israeli reports credible, and wants to see a full UN investigation.

British Prime Minister David Cameron said the news was “extremely serious” and backed Obama’s stance that the international community must respond if the reports proved accurate.

Baird was noncommittal about a military action, but expressed concern over the accusations and said Canada would work with its allies to agree on a response.

U.S. military response a certainty, expert says

But U.S. military intervention now looks inevitable says Fawez Gerges, professor of Middle East politics at the London School of Economics and Political Science.

“I believe that the U.S. now is preparing the ground for military action,” he told CBC News. “This is a matter of when, as opposed to if. What we have seen in the last 24 hours tells me that U.S. will most likely decide on military action in the near future.”

In the Syrian capital Damascus, a government official instead accused opposition forces of using them in a March attack on the village of Khan al-Assad outside of the northern city of Aleppo.

- Read about the latest developments and important players in the Syria conflict

Both sides have accused each other of the deadly attack.

The official said the Syrian army had no need for using chemical weapons "because it is capable of reaching any area in Syria it wants" without them. He spoke to The Associated Press on condition of anonymity because he was not authorized to give official statements.

Sharif Shehadeh, a Syrian lawmaker, said the Syrian army "can win the war with traditional weapons" and has no need for chemical weapons.

Syrian official blasts U.S. 'lies'

Syria's official policy is not to confirm nor deny it has chemical weapons.

Shehadeh called the U.S. claims "lies" and likened them to false accusations that Iraq possessed weapons of mass destruction — a claim U.S. policymakers had used to justify the invasion of that country in 2003.

"What is being designed for Syria now is similar to what happened in Iraq when Colin Powell lied in the Security Council and said Iraq possesses weapons of mass destruction prior to the U.S. invasion and occupation of that country," he said.

- Nelofer Pazira wrote for CBC about shellfire and lattes in the Syrian capital

U.S. President Barack Obama has said that the use of chemical weapons would be a "red line" that could result in a significant military response. But the administration said on Thursday that the new revelation won't immediately change its stance on intervention.

On the streets of Damascus, the two-year old conflict dragged on Friday, with government troops pushing into two northern neighborhoods, triggering heavy fighting with rebels as they tried to advance under air and artillery support, activists said.

The drive was the latest in a days-long offensive by government forces in and around the capital, an apparent bid to secure Assad's main stronghold against rebel challenges.

The Britain-based Syrian Observatory for Human Rights said the fighting between rebels and soldiers backed by pro-government militiamen was concentrated in the Jobar and Barzeh areas. The Local Coordination Committees, another activist group, said troops also bombarded the nearby neighbourhood of Qaboun with mortars and multiple rocket launchers.

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  • This Friday, March 1, 2013 file citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, shows a Syrian child, injured by heavy bombing from military warplanes, in the town of Hanano in Aleppo, Syria. (AP Photo/Aleppo Media Center AMC, File)

  • In this Monday, March 4, 2013 file image taken from video obtained from Ugarit News, which has been authenticated based on its contents and other AP reporting, a statue of former Syrian President Hafez Assad is pulled down in a central square in Raqqa, Syria. (AP Photo/Ugarit News via AP video, File)

  • In this Tuesday, March. 5, 2013 file citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, shows a Syrian man sitting on a fallen statue of former Syrian President Hafez Assad in a central square in Raqqa, Syria. (AP Photo/Aleppo Media Center AMC, File)

  • Smoke rises following an explosion in the Syrian village of Jamlah in the southern province of Daraa, Syria, seen from the Israeli-controlled Golan Heights ,Thursday, March 7, 2013. (AP Photo/Ariel Schalit)

  • This file citizen journalism image taken on, Sunday, March. 10, 2013 and provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, shows Syrians standing next to dead bodies that have been pulled from the river near Aleppo's Bustan al-Qasr neighborhood, Syria. (AP Photo/Aleppo Media Center AMC, File)

  • Syrian rebels aim their weapons as they take position in a building during clashes with regime forces in the Salaheddine district of Aleppo in northern Syria on March 16, 2013. (JM LOPEZ/AFP/Getty Images)

  • Syrian rebels raise their weapons under a pre-Baath Syrian flag currently used by the opposition during an anti-regime protest in the northern city of Aleppo on March 22, 2013. (BULENT KILIC/AFP/Getty Images)

  • The coffins of Sunni Muslim cleric Mohamed Saeed al-Bouti and his grandson Ahmed al-Bouti, who both died in a suicide bomb attack, are carried during their funeral ceremony on March 23, 2013 at the Omayyad mosque in Damascus, Syria. (LOUAI BESHARA/AFP/Getty Images)

  • People mourn during the funeral ceremony of Sunni Muslim cleric Mohamed Saeed al-Bouti, who died in a suicide bomb attack, on March 23, 2013 at the Omayyad mosque in Damascus. (LOUAI BESHARA/AFP/Getty Images)

  • Grand Mufti of Syria Ahmad Badr al-Din Hassoun (L) takes part in the funeral ceremony of Sunni Muslim cleric Mohamed Saeed al-Bouti, who died in a suicide bomb attack, on March 23, 2013 at the Omayyad mosque in Damascus. (LOUAI BESHARA/AFP/Getty Images)

  • People pray in the Omayyad mosque courtyard during the funeral ceremony of Sunni Muslim cleric Mohamed Saeed al-Bouti, who died in a suicide bomb attack, on March 23, 2013 in the Syrian capital Damascus. (LOUAI BESHARA/AFP/Getty Images)

  • A rebel fighter fires towards Syrian government forces positions from a building in Saif al-Dawla district in the northern Syrian city of Aleppo on March 25, 2013. (BULENT KILIC/AFP/Getty Images)

  • A Rebel scouts the positions of Syrian government forces at Saif al-Dawla district in the northern Syrian city of Aleppo on March 23, 2013. (BULENT KILIC/AFP/Getty Images)

  • Rebels clash with Syrian government forces at Saif al-Dawla district in the northern Syrian city of Aleppo on March 23, 2013. (BULENT KILIC/AFP/Getty Images)

  • In this Monday March 25, 2013, citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, anti-Syrian regime protesters burn a portrait for Syrian President Bashar Assad during a protest, in Aleppo, Syria. The Arabic on the poster reads, the dog of Iran." (AP Photo/Aleppo Media Center, AMC)

  • An rebel sniper aims at Syrian government forces positions from a hall in Saif al-Dawla district in the northern Syrian city of Aleppo on March 25, 2013. (BULENT KILIC/AFP/Getty Images)

  • In this Sunday, March 24, 2013 image taken from video obtained from the Ugarit News, which has been authenticated based on its contents and other AP reporting, Free Syrian Army fighters drops a shell into a firing tube, in Damascus countryside, Syria. (AP Photo/Ugarit News via AP video)

  • In this image taken from video obtained from the Ugarit News, which has been authenticated based on its contents and other AP reporting, Free Syrian Army fighters aim their weapons during clashes, in Damascus countryside, Syria on Monday, March 25, 2013. (AP Photo/Ugarit News via AP video)

  • In this Thursday March 28, 2013 image taken from video obtained from the Ugarit News, which has been authenticated based on its contents and other AP reporting, shows a building at the Syrian government checkpoint on fire, in Dael less than 15 kilometers (10 miles) from the Jordanian border in Daraa province, Syria. Thursday, March 28, 2013. (AP Photo/Ugarit News via AP video)

  • In this Thursday March 28, 2013 image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, shows fighters from the Syrian Free Army firing on a Syrian army position in Dael less than 15 kilometers (10 miles) from the Jordanian border in Daraa province, Syria. Syrian rebels on Friday captured a strategic town near the border with Jordan after a day of fierce clashes that killed at least 38 people, activists said, as opposition fighters expand their presence in the south, considered a gateway to Damascus.(AP Photo/Shaam News Network via AP video)

  • In this Thursday March 28, 2013 image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, shows Syrian Free Army fighters in Dael less than 15 kilometers (10 miles) from the Jordanian border in Daraa province, Syria. (AP Photo/Shaam News Network via AP video)

  • In this image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, smoke rises from buildings due to shelling in Damascus, Syria, on Thursday, March 28, 2013. (AP Photo/Shaam News Network via AP video)

  • In this photo released by the Syrian official news agency SANA, plastic tables and chairs turned upside down, are seen on the floor of the open-air cafeteria at Damascus University in the central Baramkeh district, in Damascus, Syria, Thursday, March 28, 2013. (AP Photo/SANA)

  • In this image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, a dead body lays on a street due to heavy fighting between Free Syrian Army fighters and government forces in Damascus, Syria, on Thursday, March 28, 2013. (AP Photo/Shaam News Network via AP video)

  • This citizen journalism image provided by The Syrian Revolution which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding a banner and Syrian revolution flags, during a demonstration in the town of Haas in the northwestern province of Idlib, Syria, Friday, March. 29, 2013. The banner in Arabic reads: "We will continue despite killing us. We will continue although we were betrayed. We will continue and God is with us. Good news to those who are patient." (AP Photo/The Syrian Revolution)

  • This citizen journalism image provided by Edlib News Network, ENN, which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding a placard, during a demonstration, in the town of Kafr Nabil, Idlib province, northern Syria, Friday, March. 29, 2013. (AP Photo/Edlib News Network ENN)

  • This citizen journalism image provided by Edlib News Network, ENN, which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding a placard, during a demonstration in the town of Haas in the northwestern province of Idlib, Syria, Friday, March. 29, 2013. (AP Photo/Edlib News Network ENN)

  • This citizen journalism image provided by The Syrian Revolution which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding banners and Syrian revolution flags, during a demonstration in the neighborhood of Bustan Al-Qasr in Aleppo, Syria, Friday, March. 29, 2013. (AP Photo/The Syrian Revolution)