Israel's military said on Wednesday it believes Syrian President Bashar Assad's forces still possess several tons of chemical weapons, issuing the assessment two weeks after a sarin attack that killed nearly 90 people in Syria.

Israel, along with many countries, blames the strike on Assad's military. French Foreign Minister Jean-Marc Ayrault said French intelligence services would provide proof of that in the coming days.

A senior Israeli military officer, in a briefing to Israeli reporters, said "a few tonnes of chemical weapons" remained in the hands of Assad's forces, a military spokesman told Reuters.