08/28/2013 03:58 EDT | Updated 10/27/2013 05:12 EDT

Syria attack involved chemical 'substance,' UN envoy says

The UN says a toxic "substance" was deployed last week in Syria and it "killed a lot of people," supporting growing international claims that chemicals were used in an attack near Damascus.

UN special envoy to Syria Lakhdar Brahimi made the comment Wednesday. However, the source of the attack has not been confirmed, as the UN inspectors' role in collecting evidence of chemical use doesn't include determining who is behind it.

The Arab League as well as Western powers have held President Bashard al-Assad's forces responsible for using toxic agents to kill hundreds of people in the Aug. 21 assault, but Assad has denied the allegations.

Brahimi, however, said: "It does seem that some kind of substance was used that killed a lot of people. This confirms how dangerous the situation in Syria is."

The UN team's first field testing was in the western Damascus suburb of Moadamiyeh on Monday. The journey was delayed by sniper fire, though the team was unharmed. On Wednesday, the UN's convoy of seven SUVs again left a hotel in central Damascus to resume inspections.

According to anti-regime activitists, the inspectors made their way this time to the Damascus suburb of Eastern Ghouta, which was affected by the alleged chemical attack.

Inspectors have not accused rebel fighters or government troops of using chemical weapons in an attack that Doctors Without Borders says killed 355 people.

To the White House, though, it's "undeniable" that the government is the only side capable of launching a chemical attack, according to U.S. Secretary of State John Kerry.

Amid ramped-up rhetoric from Western allies for building military action against Syria, Braihimi reitereated that any military action must have approval at the UN Security Council level.

"I do know that…Obama and the American administration are not known to be trigger-happy," Brahimi said. "What they would decide, I don't know, but certainly international law is very clear — the Security Council has to be brought in."

Although the Arab League has condemned the Syrian government, is has not offered regional support to a retaliatory military strike.

Jordan's information minister said Wednesday his government "will not be a launching pad for any military action against Syria" and favours a diplomatic solution.

Poland has taken the same position, with Prime Minister Donald Tusk saying it will not participate "in any kind of intervention" in Syria.

British Prime Minister David Cameron's office said in a statement Wednesday it will put forward a draft resolution under Chapter 7 of the UN charter.

Cameron's office said Britain seeks a measure "authorizing necessary measures to protect civilians," and that military force is one of the options that can be authorized.

"We have always made clear that we want the UN Security Council to live up to its responsibilities on Syria. Today we are giving its permanent members the opportunity to do that," a Downing Street spokesperson said in a statement.

However, any language that could be read as allowing a military strike is likely to face veto by Syria's allies, Russia and China.

Canada says suspected chemical use 'an outrage'

Canadian Foreign Affairs Minister John Baird has called the alleged chemical attack an "outrage" and Prime Minister Stephen Harper is conferring closely with U.S. President Barack Obama as the Syrian situation escalates.

A branch of the jihadist group Islamic State in Iraq and the Levant (ISIL) issued a statement pledging to punish Assad's forces by striking government targets in an impending assault. The threat was reported by the SITE intelligence group, which tracks online terrorist activities.

ISIL claimed to have met with eight Syrian factions about a series of massacres by government forces.

"The meeting factions decided to carry out the 'volcano of revenge' invasion in response to the regime's massacres against our people in Eastern Ghouta, the last of which was the chemical weapons massacre," SITE quoted the statement as saying.

"They have decided to strike the main joints of the regime in imprisoned Damascus, including security branches, support and supply points, training centres, and infrastructure," the statement said.