France was set Monday to provide what it says is clear evidence that the Syrian regime was behind a devastating chemical attack, as Western leaders bid to overcome widespread scepticism to military action.
With US President Barack Obama also lobbying Congress to back strikes, the Syrian regime said it remained on alert for a possible attack, urging the United Nations to "prevent any aggression" against it.
NATO chief Anders Fogh Rasmussen said he was personally convinced the chemical attack had taken place and that Syrian President Bashar al-Assad's regime was responsible.
He called for a response that would "send a very clear message" against the use of chemical weapons, but said any military action should be "very short, sharp (and) tailored".
French government sources said evidence proving the regime's involvement in the attack would be provided to top lawmakers at a meeting with Prime Minister Jean-Marc Ayrault at 1500 GMT.
"We are going to give parliamentarians everything that we have -- classified until now -- so that each of them can take into account the reality of this unacceptable attack," Ayrault said.
A government source said lawmakers would be given "evidence of different kinds that will allow the regime to be clearly identified as responsible for the August 21 chemical attack".
The French parliament is to hold a debate Wednesday on taking action on Syria, where more than 110,000 people have been killed in violence since an uprising against the regime began in March 2011.
Government sources said Sunday that French intelligence had compiled information showing the Syrian regime had stockpiled more than 1,000 tonnes of chemical agents, including sarin gas, mustard gas and more powerful neurotoxic agents.
Hollande has vowed to "punish" Assad for the alleged gas attack, which Washington says killed more than 1,400 people.
The French president can order military action without parliamentary approval but some lawmakers have urged Hollande to put the issue to a vote, as Obama is doing in the United States.
France has emerged as the main US ally in the Syria crisis after the British parliament, in a shock move, rejected plans for military action mooted by Washington.
Britain's government said Monday it had "no plans" to hold a second parliamentary vote on joining military action.
But public opinion in both France and the US is deeply sceptical, and in a surprise move Obama put off threatened missile strikes, saying Saturday he would seek approval from Congress first.
That pushed back any US-led military action until at least September 9, when US lawmakers return from their summer break.
Obama and other top administration officials lobbied individual members of Congress in calls on Sunday, saying Washington had proof the Damascus regime used sarin gas in the attack.
More calls were planned for Monday, a US holiday.
A Syrian security official told AFP that the country's army was still "on alert", even if the threat of an imminent strike had receded.
State news agency SANA reported that Damascus had urged UN Secretary General Ban Ki-moon to "assume his responsibilities... and to make efforts to prevent any aggression against Syria."
Assad ally Russia meanwhile said it remained unconvinced that the regime carried out the attack, warning that Western military action would sink joint efforts by Washington and Moscow to organise a peace conference in Geneva.
"If the action announced by the US president -- to the great regret of all of us -- does in fact take place... it will put off the chances of (holding) this conference for a long time, if not forever," Foreign Minister Sergei Lavrov said.
China, which in the past has joined Russia in blocking UN Security Council resolutions against Assad, also said it was "gravely concerned" about the prospect of "unilateral military actions" against Syria.
Five US destroyers are currently positioned in eastern Mediterranean waters, up from the usual three that normally focus on countering Iranian ballistic missile threats to Europe.
ABC News reported Monday that the USS Nimitz aircraft carrier was also moving westward toward the Red Sea, although it has not yet received orders to support a potential US strike on Syria.
Witnesses in Lebanon reported that the Shiite Hezbollah group, a close ally of the Syrian regime, was redeploying its forces ahead of possible US strikes.
The reports came as the daily Al-Akhbar, which is close to both Hezbollah and the Syrian regime, said that the group had "called on all its officers and members to man their positions."