Turkey's president has announced that a Turkish military helicopter was "downed" in northern Syria during Ankara's offensive on Syrian Kurdish militia in the region.

Analysis of samples taken from a deadly sarin gas attack in Syria earlier this month "bears the signature" of President Bashar Assad's government and shows it was responsible for the deadly assault, France's foreign minister has said.

Turkish jets and artillery have struck US-backed Syrian Kurdish fighters in northern Syria, killing as many as 200 fighters, according to Turkey's state-run news agency.