White House spokesman Jay Carney said that "it's in the clear national interests" of the United States to punish Syria's regime for what he called a "repugnant" chemical attack on Syrians, and that the question now is how the U.S. will respond to a violation of international norms.

"Broadly speaking, I think it's important to note that it's in the clear national interests of the United States that the use and proliferation of chemical weapons on this scale not go unanswered," Carney told reporters Tuesday, referring to reports that Assad's government has used chemical weapons to kill hundreds of its own people.

Carney said it was a "repugnant fact" that toxic agents were used in an attack last week against "innocent Syrians."

"The Assad regime is the only possible force that could have deployed

[chemical weapons]," Carney said. "There has to be a response to that clear violation of international norms."

However, Carney would not say what that response would be, or whether it would involve military action from the U.S.

"A course of action has not been decided upon. When the president has an announcement to make, he'll make it," he said.

Later Tuesday, U.S. Vice-President Joe Biden said there was no question Assad was responsible for the attack, becoming the highest ranking U.S. official to say so. He said the Syrian government is the only actor in the conflict that possesses chemical weapons and can deliver them.

Possible strike in 'next few days'

Syrian opposition leaders have been told to prepare for a Western-backed assault on Assad's regime within a matter of days, according to sources who attended a meeting with the Syrian National Council in Turkey.

"The opposition was told in clear terms that action to deter further use of chemical weapons by the Assad regime could come as early as in the next few days, and that they should still prepare for peace talks at Geneva," one of the sources who was at the meeting with the Syrian on Monday told Reuters.

Reuters reported that the notice came from "Western powers" and that Syrian opposition leaders have also handed over a wish list of targets should a possible strike be imminent.

The U.S. navy has four destroyers positioned in the eastern Mediterranean Sea, within range of targets in Syria, according to the U.S. Department of Defence. American warplanes are already in the region.

Malcolm Chalmers, a researcher with a U.K.-based organization that focuses on defence and security, told CBC News he believed the target of a U.S.-led strike would likely be cruise missile strikes on conventional forces in Syria.

"But it may also be command-control facilities," Chalmers said, adding that he thinks an attack of that scale "will not destroy the regime."

Syrian Foreign Minister Walid al-Moallem, however, warned that any U.S. or European military intervention would also be met with force through "all available means."

Moallem addressed a news conference Tuesday after U.S. Secretary of State John Kerry stopped short of saying President Barack Obama was ready to take military action in Syria. 

Kerry has strongly condemned what he called "undeniable" evidence that Syria launched a chemical attack last week that killed hundreds of people in three Damascus suburbs — a claim that a special UN convoy began investigating on Monday but that Syria has denied.

On Tuesday, the Arab League joined western nations in laying blame on the Syrian government for the alleged chemical weapons attack. The 22-member body backed the calls to punish Assad's government for the "heinous crime."

'We will surprise everyone'

Moallem told reporters in Damascus that "we have the means to defend ourselves and we will surprise everyone." 

"We will defend ourselves using all means available. I don't want to say more than that," he added.

The strong words from Syria are not to be taken lightly by any military, as the country's force is considered to be much more formidable than the Libyan army, which U.S. airstrikes were able to neutralize two years ago. 

The UN, which sent a convoy of investigators to Damascus on Monday to launch a probe into whether chemical weapons were used by Syria last week, says more than 100,000 people have been killed since the uprising against President Bashar al-Assad began more than two years ago.

A second round of UN inspections that was to begin Tuesday has been pushed back until at least Wednesday due to a dispute with rebels about security arrangements, he added. The UN confirmed the delay.

'Most heinous weapons'

Moallem blamed the delay on rebel fighters, claiming that the opposition has not yet promised safe passage to the UN experts, and that the inspections will not be able to proceed until at least Wednesday as a result. Moallem did not elaborate on the postponement of the UN trip.

Assad has denied launching a chemical attack, blaming "terrorists" for the incident.

However, the regime prevented UN inspectors from visiting the site of the Aug. 21 attack until Monday. The team reached the site despite coming under fire from a sniper and was able to speak with survivors and physicians who treated the victims. They also used instruments to try to determine what chemical agent was used.

U.S. 'ready to go'

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U.S. Secretary of Defence Chuck Hagel says American military is in a position to move as soon as the president gives the go-ahead. (Reuters)

American forces are poised to strike in Syria at any moment and are awaiting President Barack Obama's order, according to the U.S. secretary of defence.

In an interview with BBC television, Chuck Hagel said the U.S. has "moved assets in place" amid "good intelligence" that chemical weapons were indeed used against people in Syria.

"We are prepared. We are ready to go," he told the BBC, according to a transcript provided to Reuters. 

On Monday, Kerry said Obama has been in close touch with key Western allies, and "will be making an informed decision about how to respond" to what the U.S. considers indiscriminate use of toxic agents against civilians.

"Make no mistake," Kerry added. "President Obama believes there must be accountability for those who would use the world’s most heinous weapons against the world’s most vulnerable people."

Two administration officials said the U.S. was expected to make public a more formal determination of chemical weapons use on Tuesday, with an announcement of Obama's response likely to follow quickly. The officials insisted on anonymity because they were not authorized to publicly discuss the internal deliberations.

U.S. Defence Secretary Chuck Hagel told BBC News in an interview that the U.S. military is in position to move as soon as the commander in chief gives the go-ahead.

"We are ready to go, just like that," he said.

Canada is weighing all options, and Chief of the Defence Staff Gen. Thomas Lawson is in a third day of key military meetings with joint chiefs of staff in Jordan. The purpose of the meeting is to ensure the allied mlitary chiefs are able to devise a strategy for containing any possible conflict to Syria and preventing spillover into neighbouring regions. 

Harper and Obama to 'consult closely'

Prime Minister Stephen Harper and Obama spoke on the phone Tuesday about their "grave concern" about the escalating situation in Syria, according to a spokesperson with Harper's office in Ottawa. 

"The United States and Canada strongly oppose the use of chemical weapons, and the president and prime minister pledged to continue to consult closely on potential responses by the international community," a statement from the White House Press Office said.

Canadian Foreign Affairs Minister John Baird has said Canada is "incredibly outraged" by the purported use of chemical weapons in Syria, and that a "firm response" from the international community should be expected.

While Baird has expressed a preference for a UN mandate, he has not ruled out any role Canada might play in a possible military strike.

France is prepared to boost its military support of the opposition, and President François Hollande said it is "ready to punish" those responsible for what he called a "chemical massacre."

In London, British Prime Minister David Cameron has recalled Parliament for an urgent discussion on a possible military response to the alleged chemical attack in Syria.

Cameron says the crisis session will be held Thursday, when Parliament would traditionally be on its summer recess.

'President Obama believes there must be accountability for those who would use the world’s most heinous weapons against the world’s most vulnerable people.'—U.S. Secretary of State John Kerry

It's unclear whether Obama would seek authority from the United Nations or Congress before using force. The president has spoken frequently about his preference for taking military action only with international backing, but it is likely Russia and China would block U.S. efforts to authorize action through the UN Security Council.

The U.S. State Department on Monday postponed a meeting scheduled for Wednesday in The Hague between senior diplomats from the United States and Russia due to "ongoing consultations" over the chemical weapons attack in Syria.

"We will work with our Russian counterparts to reschedule  the meeting," the senior official said, adding that the chemical weapons attack demonstrated the need for a "comprehensive and  durable political solution" to end the bloodshed.

Russia responded on Tuesday that it regretted the decision.

With files from Reuters, The Associated Press