Syrian President Bashar al-Assad has challenged the U.S. and France to provide evidence his regime used chemical weapons on civilians in August, warning that any strikes on his country would result in dire repercussions, and "chaos and extremism" would spread.

"Those who make accusations must show evidence," Assad said in an interview with the French newspaper Le Figaro.

"We have challenged the United States and France to come up with a single piece of proof," he said in excerpts published Monday in the daily.

Assad said U.S. President Barack Obama and French President Francois Hollande "have been incapable" of proving Syria was behind a chemical attack on Aug. 21, allegations the Syrian president has repeatedly denied.

The interview with Assad was published as Obama set out on Labour Day Monday to persuade congressional leaders to approve strikes against the Syrian military for the alleged chemical attack that the U.S. has said killed more than 1,400 people, about a third of them children. Obama, in an emotional and hard-nosed speech on Saturday, said the U.S. should take military action against Syria, but that he will seek approval from Congress when it returns to business Sept. 9.

But Assad said in his Le Figaro interview: "Anybody who contributes to the financial and military reinforcement of terrorists is the enemy of the Syrian people. If the policies of the French state are hostile to the Syrian people, the state will be their enemy. There will be repercussions, negative ones obviously, on French interests."

He also warned that "the whole world will lose control of the situation. Chaos and extremism will spread."

U.S. Senators speak on Syria

Later Monday, U.S. Senators John McCain and Lindsey Graham said it would be a mistake for Congress to reject Obama's request.

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Senator John McCain, a Republican from Arizone, left, accompanied by Senator Lindsey Graham, a Republican from South Carolina, speaks with reporters outside the White House in Washington. (Evan Vucci/Associated Press)

"We have to make it clear that a vote against this would be catastrophic in its consequences," now and in future international crises, McCain told reporters outside the White House following a private meeting that he and Graham had with Obama.

Said Graham: "A degrading strike limited in scope could have a beneficial effect to the battlefield momentum. There will never be a political settlement in Syria as long as Assad is winning."

McCain and Graham have called on Obama to launch comprehensive military strikes with an aim of destroying Assad's air power, his military command and control, Syria's ballistic missiles and other military targets while giving opposition forces more arms and training. But some Republican and Democratic lawmakers don't want to see military action at all.

Earlier on Monday, Syria pressed UN Secretary General Ban Ki-moon "to shoulder his responsibilities for preventing any aggression" against the country. Bashar Ja'afari, Syrian envoy to the UN, also said in a letter to Ban and Security Council President Maria Cristina Perceval that the UN needs to push towards "reaching a political solution to the crisis in Syria," state news agency SANA said.

The letter from Ja'afari calls on the Security Council to "maintain its role as a safety valve to prevent the absurd use of force out of the frame of international legitimacy." He also said the U.S. should only "play its role, as a peace sponsor and as a partner to Russia in the preparation for the international conference on Syria and not as a state that uses force against whoever opposes its policies."

The UN estimates the uprising has led to the deaths of more than 100,000 people. As well, the UN refugee agency released figures Monday showing that nearly one-third of the population — about seven million Syrians — has been displaced since the uprising against Assad began in March 2011.

UN refugee agency spokesman Tarik Kurdi said five million of the seven million displaced Syrians are still in the country, and that about two million have taken refuge in neighbouring countries. As well, two million of those directly affected by the war are children.

Kurdi told The Associated Press that UN assistance has been a "drop in the sea of humanitarian need," and that the funding gap is "very, very wide." He says international donors have sent less than one-third of the money needed to help those displaced by the war.

Obama seeks congressional support

The situation in Syria began heating up late last week, with Secretary of State John Kerry releasing figures that the U.S. says show 1,429 people were killed by chemicals in the August attack. Doctors Without Borders pegs the death toll at much less.

A UN team spent four days in Syria investigating claims of chemical weapons use, and briefed Ban on preliminary information about their findings, UN’s media office said.

UN investigators examined the area of the alleged gas attack for four days. They left Syria on Saturday for The Hague, where their findings were to be sent to laboratories around Europe for analysis.

The Organization for the Prohibition of Chemical Weapons based in The Hague says examination of evidence could take up to three weeks.

Obama made it clear Saturday, when he spoke on the White House lawn, that he supports direct military action in Syria, saying chemical weapons use amounts to a "serious danger" to national security and "an assault on human dignity."

However, Obama added that he would turn to Congress to get the go-ahead to take any military action, and that it will be ready to debate and vote on the issue when it resumes Sept. 9. U.S. navy ships in the Mediterranean Sea are ready to strike, said Obama, who has the power to unilaterally order an attack. However, he said, he has determined that the U.S. "will be better off" if Congress comes up with its own opinion.

While the U.S. is seeking allies to come onboard for action against Syria, Obama's attempt to garner support took a blow Friday when British politicians voted against any military response. Prime Minister David Cameron lost the vote 285-272, and said later that while he "strongly" believes in the need for a tough response to chemical weapons use, he also believes in respecting the will of the House of Commons.

In Canada, Prime Minister Stephen Harper has also said that the country has no plans for a military mission of its own in Syria, but said the government supports its allies and has been convinced of the need for "forceful action."

Russian President Vladimir Putin, meanwhile, reacting to a proposal by two Russian legislators, said Monday he hopes to send some lawmakers to the U.S., to try to persuade legislators to take a "balanced stance" on the Syria issue.

The Russian news agency Interfax said Putin supported the proposal by Valentina Matvienko and Sergei Naryshkin. The proposal, which requires formal approval by the Foreign Ministry, follows polls that have shown little support among Americans for armed intervention in Syria.

Russia is a loyal Assad ally, and Putin had already said on the weekend that the idea of a U.S. military intervention in Syria would be "foolish nonsense" that "defies all logic."

On Monday, Russian Foreign Minister Sergey Lavrov said evidence presented by the U.S. to Moscow of the alleged chemical weapons use by the Syrian regime as "absolutely unconvincing. There was nothing specific there, no geographic co-ordinates, no names, no proof that the tests were carried out by the professionals."

Just want to live 'peacefully'

The head of NATO, Secretary General Anders Fogh Rasmussen, also weighed in Monday, saying that "personally, I am convinced, not only that a chemical attack has taken place ... but I am also convinced that the Syrian regime is responsible."

Rasmussen said dictators around the world need to be sent a message that such weapons cannot be used with impunity. He also said NATO would remain a strong defender of Turkey if the member state was attacked as part of the Syria crisis, and it would remain a forum for allies to consult about action. However, he added, he does not see an additional NATO role.

Syrian Dr. Mohammed Abu Omar, who lives in Moadamia City, a western suburb of Damascus, was reached by Derek Stoffel, Middle East correspondent for CBC News, to describe the horrors facing the people of Syria. 

Omar said via Skype that Syrians welcome military intervention, but until now, "we didn’t have the trust in the West to do that, because we have two years of being killed at every moment and no one wants to stop the killer – Bashar [al-Assad’s]

regime."

Speaking about the dire situation in Syria, the doctor said: "We don’t have food. We don’t have medical supplies. We are under siege since 10 months ago. We are under huge shelling every day. We are being killed every single moment. ... We just want to live the rest of our lives peacefully, without getting killed in every single moment."

With files from The Associated Press, Reuters