Syrian President Bashar al-Assad scorned allegations that his forces were behind the chemical attack in Damascus last month and warned that any French military action against his government would lead to "negative repercussions".
President Francois Hollande, along with U.S. President Barack Obama, has said Assad should be punished for the August 21 attack in which Washington says more than 1,400 people, many of them children, were killed. The Syrian government says it was carried out by rebels - who it often refers to as "terrorists".
Assad said it would have made no sense to use chemical weapons in an area where his troops were also fighting.
"Those who make accusations must show evidence. We have challenged the United States and France to come up with a single piece of proof. Obama and Hollande have been incapable of doing so," he said in an interview with French daily Le Figaro.
"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," he said. "There will be repercussions, negative ones obviously, on French interests."
France has backed the Syrian rebels since the start of the two-and-a-half year old conflict. It is worried that spiraling violence could spill into Lebanon, where about 20,000 French nationals live and many French companies operate.
Diplomatic sources say Paris fears Assad's forces could attack its interests there in retaliation for Western strikes.
"The Middle East is a powder keg and the fire is approaching," Assad said, according to extracts of the interview published on Monday.
"We shouldn't just talk about a Syrian response, but what will happen after the first strike. Everybody will lose control of the situation when the powder keg blows."
Senior members of France's ruling party rebuffed opposition calls for a parliamentary vote on whether to take military action against Syria, saying on Monday lawmakers should respect the president's constitutional right to decide on attacks.