TORONTO - The crisis in Syria has entered a "dangerous new phase," Foreign Affairs Minister John Baird warned Monday, as Washington announced it had "undeniable" evidence of a chemical weapons attack.

Baird condemned "in the strongest terms" a sniper attack on a United Nations convoy carrying a team investigating the alleged chemical attack, which Syrian activists claim killed hundreds of civilians.

"The attacks on the United Nations convoy in Damascus are absolutely abhorrent," Baird said.

"The Syrian regime has the fundamental duty to protect these individuals, these representatives of the United Nations and the international community."

U.S. Secretary of State John Kerry declared Monday that there was "undeniable" evidence of a large-scale chemical weapons attack in Syria.

"The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity," Kerry said.

The Syrian government accused rebel forces of firing at the UN team, while the opposition said a pro-government militia was responsible.

Baird declined to call for military intervention in Syria. Meanwhile, Western support mounted for an international military response if it is confirmed that President Bashar Assad's troops used chemical weapons.

"I think first we're going to work to get the facts with the UN team on the ground," Baird said.

"We have been in close contact, both the prime minister and I, with three of our main allies in this regard. We'll work with them and when we have additional things to report we will do so."

Opposition Leader Thomas Mulcair said he supports first working through international law, and taking it one step at a time, but didn't rule out future military intervention.

American officials said President Barack Obama has not decided how to respond to the use of deadly gases, a move the White House said last year would cross a "red line."

France, Britain, Israel and some U.S. congressmen have said a military response against the Syrian regime should be an option. Russia, however, has said that Western nations calling for military action have no proof the Syrian government was behind any chemical attacks.

Baird said Canada will continue working with its international partners to "review a full range of options."

"Canada believes the only way to halt the bloodshed in Syria is through a political solution," he said. "However, we understand that this solution is becoming more and more difficult as the crisis enters a very dangerous new phase."

He called on Russia to end its "complete obfuscation" and become part of the solution.

The UN inspectors are attempting to examine the site of the Aug. 21 attack in the capital's suburbs.

Delay tactics used by the Assad regime in giving UN inspectors access has likely already impaired the UN team's ability to assign responsibility, Baird said. Still, he called on Syrian authorities to allow the team unfettered access.

The U.S. said Syria's delay in giving the inspectors access rendered their investigation meaningless and officials said the administration had its own intelligence confirming chemical weapons use.

The assessment is based in part on the number of reported victims, the symptoms of those injured or killed and witness accounts. Kerry said the administration also had additional intelligence and would make its findings public soon.

Assad has denied launching a chemical attack and his government vowed to defend itself against any international attack, warning that such an intervention would ignite turmoil across the region.

More than 100,000 people have been killed in Syria since Assad cracked down on Arab Spring-inspired protesters in March 2011.

— With files from The Associated Press

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