French intelligence services will provide proof in the coming days that Syrian President Bashar al-Assad's forces used chemical weapons in an attack on April 4, French Foreign Minister Jean-Marc Ayrault says.
"There is an investigation underway (by) the French intelligence services and military intelligence ... it's a question of days and we will provide proof that the regime carried out these strikes," Mr Ayrault told LCP television on Wednesday.
"We have elements that will enable us to show that the regime knowingly used chemical weapons," he said.
Mr Assad claims the poison gas attack is a fabrication used to justify the US air strike.
He told media Syria's military gave up all its chemical weapons in 2013 "and would not have used then anyway."
At least 86 people, including 30 children, were killed in the chemical attack on Khan Shaykhun, a rebel-held area in north-western Syria, the Syrian Observatory for Human Rights reports.
The Turkish government said autopsies on victims brought over the border confirmed chemical weapons had been used.