President Bashar al-Assad warned the US of "failure" if it attacks Syria, as UN experts begin probing allegations Syrian forces used chemical weapons on civilians.
In an escalation of a showdown over the suspected attack near Damascus last week, the United States and its Western allies pointed the finger of blame at Assad's regime.
The Syrian president, in an interview with a Russian newspaper published on Monday, angrily dismissed the allegations as an "insult to common sense".
Assad told pro-Kremlin daily Izvestia that the frontline in the area where the incident took place was not clear and the Syrian regime would have risked killing its own troops if it used chemical weapons.
"The comments made by politicians in the West and other countries are an insult to common sense... It is nonsense," he said.
Assad warned the United States against attacking Syria and argued Washington's recent military campaigns had all fallen short of their aims.
"The United States faces failure just like in all the previous wars they waged, starting with Vietnam and up to our days," he said.
A US diplomatic offensive led by Secretary of State John Kerry, comments coming from the White House and signs the Pentagon is positioning ships closer to Syria fuelled an impression that President Barack Obama may be getting ready to jettison his antipathy to new Middle Eastern entanglements and to order limited military action.
Kerry has spent days on the phone with Washington's foreign partners.
French President Francois Hollande told his US counterpart that "everything was consistent" with the conclusion that Damascus was behind the attack.
"The two presidents agreed to stay in close contact to arrive at a joint response to this unprecedented aggression," the French leader's office said.
Russian Foreign Minister Sergei Lavrov warned Kerry of the "extremely dangerous consequences" of launching military action.
Lavrov told Kerry in a telephone call on Sunday that Moscow was "deeply alarmed" by statements coming out of Washington.
"Sergei Lavrov drew attention to the extremely dangerous consequences of a possible new military intervention for the whole Middle East and North Africa region," a Russian foreign ministry statement said.
Syria's opposition says more than 1,300 people died when toxic gases were unleashed last Wednesday as regime forces bombarded rebel zones east and southwest of Damascus before dawn.
Doctors Without Borders said 355 people had died of "neurotoxic" symptoms in the affected areas.
If confirmed, the attack would mark the deadliest use of chemical agents since Iraqi dictator Saddam Hussein gassed Iranian troops and Kurdish rebels in the 1980s.
The Syrian authorities green-lighted the UN inspection on Sunday, but US officials said it was too little, too late, arguing that persistent shelling of the site in recent days had "corrupted" the site.
British Foreign Secretary William Hague too warned any evidence of a chemical attack may have been destroyed by the artillery bombardment.
UN chief Ban Ki-Moon said Monday there was no time to waste in probing the allegations.
"Every hour counts. We cannot afford any more delays," Ban told reporters in Seoul as UN experts prepared to travel to the site of the alleged attacks.
French Prime Minister Jean-Marc Ayrault implied that a punitive strike on Syria was not imminent, in an interview with France 2 television.
"Once this (UN) investigation has ended, we await a firm decision, a clear decision, from the international community. The (UN) Security Council will meet," he said.
More than 100,000 people have been killed in Syria since an uprising against Assad's rule flared in March 2011, the UN says.
