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".
"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.
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.
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.
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