His remarks were released as United Nations chemical weapons inspectors met and took samples from victims of the apparent poison gas attack in a rebel-held suburb of Damascus after the UN team itself survived a gun attack on their convoy.
Assad told Russia's Izvestia daily that the accusations that his troops were responsible were "politically motivated."
"This is nonsense," Assad was quoted as saying. "First they level the accusations, and only then they start collecting evidence."
Assad said that attacking such an area with chemical weapons would not make sense for the government as there was no clear frontline between regime and rebel forces.
"How can the government use chemical weapons, or any other weapons of mass destruction, in an area where its troops are situated?" he said. "This is not logical. That's why these accusations are politically motivated, and a recent string of victories of the government forces is the reason for it."
A United States official said Sunday that there was "very little" doubt that Assad's regime was responsible for the August 21 attack.
Anti-government activists and Doctors without Borders say that more than 300 people were killed in an artillery barrage by regime forces Wednesday that included the use of toxic gas.
UN inspectors reach attack site
Also on Monday, a Syrian doctor from the town of Mouadamiya told Reuters that investigators from the United Nations had crossed the frontline from the center of the capital, which remains under the control of Assad's forces.
The team not deterred by a shooting that crippled one vehicle but caused no injuries. Syrian state television blamed rebel "terrorists" for the attack, while the opposition blamed it on pro-Assad militiamen. Any delay diminishes whatever evidence the experts might recover.
"I am with the team now," the doctor, who uses the name Abu Karam, told Reuters by telephone from rebel-held Mouadamiya.
"We are in the Rawda mosque and they are meeting with the wounded. Our medics and the inspectors are talking to the patients and taking samples from the victims now."
There was a plan for the experts also to take samples from corpses.
On Sunday, Syria said that a UN team could investigate the site, but a senior White House official dismissed the deal as "too late to be credible."
With France, Britain, Israel and some U.S. congressmen urging swift military action against Assad's regime if the use of chemical agents is confirmed, the UN team's conclusions could have a dramatic impact on the trajectory of the country's civil war.
U.S. weighing options
U.S. Defense Secretary Chuck Hagel said on Monday any operation would be coordinated with allies. British Prime Minister David Cameron cut short a holiday to chair a top level security meeting.
"The United States is looking at all options regarding the situation in Syria. We're working with our allies and the international community," Hagel told a news conference.
"We are analyzing the intelligence. And we will get the facts."
French Foreign Minister Laurent Fabius said no decision had been made on a military intervention but that any response would be "proportionate."
"It will be negotiated in coming days," Fabius told Europe 1 radio on Monday. He said that the lack of a UN blessing was problematic, but that all options remain on the table. "The only option that I can't imagine would be to do nothing," Fabius said.
Russia, which has been a staunch ally of Syria, said last week that the accusations against Assad could be a bid to get the Security Council to stand by the opposition, and to undermine efforts to resolve the conflict by convening a peace conference in Geneva.
Security Council backing not needed
British Foreign Secretary William Hague said on Monday it would be possible to respond to chemical weapons use in Syria without the unanimous backing of the United Nations Security Council.
"Is it possible to respond to chemical weapons without complete unity on the UN Security Council? I would argue yes it is, otherwise it might be impossible to respond to such outrages, such crimes, and I don't think that's an acceptable situation," Hague said on BBC radio.
Turkey announced it would join any international coalition against Syria even if a wider consensus on action cannot be reached at the UN Security Council, Foreign Minister Ahmet Davutoglu was quoted as saying on Monday.
"We always prioritize acting together with the international community, with United Nations decisions. If such a decision doesn't emerge from the UN Security Council, other alternatives ... would come onto the agenda," Davutoglu told the Milliyet daily.
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