US, Russia trade threats at UN Security Council over Syria

The United States has told the United Nations Security Council Washington will respond to an alleged chemical weapons attack on a rebel-held town in Syria, regardless of whether the UN acts or not.

Russia's UN Ambassador, Vassily Nebenzia Source: AAP

But Russia is warning the US of "grave repercussions" if it carries out an attack against the Syrian government.

The United Nations special envoy for Syria, Staffan de Mistura, has called on the Security Council to conduct a thorough investigation of the alleged attack.

Since the conflict began in Syria in 2011, the United Nations estimates more than 470,000 people have been killed, with millions of Syrians displaced internally and abroad as a result of the conflict.