US threatens military response to Syria chemical attack

The United States has threatened Syria with military action as President Donald Trump warned "something should happen" following a chemical attack that left at least 86 dead and provoked global outrage.

An American decision to strike the regime in Damascus could hinge on the outcome of a Security Council vote, at around 2300 GMT, on a Western resolution on the attack that could face a Russian veto.

US Secretary of State Rex Tillerson vowed an "appropriate response" to the attack in Khan Sheikhun in rebel-held Idlib province, whose victims included 27 children.

Trump has signalled a startling about-turn towards President Bashar al-Assad, who many in the international community hold responsible for Tuesday's horrific events.

"What Assad did is terrible. What happened in Syria is truly one of the egregious crimes," the US leader said on Thursday. "I guess he's running things, so I guess something should happen."

Trump's comments came as Tillerson called explicitly for "a political process that would lead to Assad leaving" and said his future role in the country was "uncertain."

It remained unclear whether Assad's main ally Russia would resort to its veto power to block the draft resolution presented to the UN, which was slightly revised following negotiations over the past two days.

Britain, France and the United States are backing the draft which demands a full investigation of the incident, which Turkey believes exposed victims to the nerve agent sarin.

The US Ambassador Nikki Haley has warned that Washington could take unilateral action if the world body fails to respond to the serious allegations of chemical weapons use.

A US official said the Pentagon is presenting the White House with a range of possible military options, including cruise missile or airstrikes on Assad's air fields in a bid to ground his air force, but that no decisions had been taken.

Any such military action brings enormous risks, as strikes could be subject to skirting Russian air defences. Moscow also has advisers on the ground in Syria.