Syrian President Bashar 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".
Meanwhile, President Francois Hollande, along with US President Barack Obama, has said Assad should be punished for the Aug. 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".
France aims to build a coalition of countries to back military action against the Syrian government in response to a chemical weapons attack in Damascus, Prime Minister Jean-Marc Ayrault said on Monday.
"This act cannot be left without a response," Ayrault said after presenting an intelligence report on Syria to lawmakers. "It's not for France to act alone. The president is continuing his work of persuasion to bring together a coalition without delay."
"France is determined to penalize the use of chemical weapons by Assad's regime and to dissuade with a forceful and firm response," Ayrault said. "The objective is neither to topple the regime or liberate the country." he said, adding that only a political solution in Syria was possible.
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.
The full Assad interview is due to be published on Tuesday.