US Ambassador Nikki Haley told the UN Security Council on Friday that it must "act now" to extend an investigation of chemical weapons attacks in Syria, a move that could be vetoed by Russia.

The United States has circulated a draft resolution extending the mandate of the joint UN-OPCW (Organisation for the Prohibition of Chemical Weapons) panel for another year and diplomats said a vote at the council could be held as early as Monday.

The measure is facing a possible veto from Russia, Syria's ally, which wants to first see a report due on Thursday on the sarin gas attack in Khan Sheikhun before deciding on the fate of the investigation.

"We must act now and support the continuation of the JIM's important work," Haley said in a letter to the council obtained by AFP.

The Joint Investigative Mechanism (JIM) was established by the council in 2015 to determine who is responsible for chemical weapons attacks in Syria's six-year civil war. Its mandate expires on November 18.

The United States accuses Russia of linking the panel's survival to its findings on the April 4 Khan Sheikhun attack.

France, Britain, and the United States have accused Assad's forces of carrying out the attack on the opposition-held village that killed at least 87 people, including more than 30 children.

Last month, UN war crimes investigators said they had evidence that the Syrian air force was behind Khan Sheikhun, despite repeated denials from Damascus.

Haley argued that the OPCW was reviewing more than 60 cases of alleged chemical weapons use in Syria, including a recently-uncovered sarin attack on an opposition-held village on March 30.

"This is not about politics or the contents of the next report, but about ensuring accountability for those who are using these terrible weapons, whether they are UN member states or non-state actors," Haley wrote.

The JIM has already determined that Syrian government forces were responsible for chlorine attacks on three villages in 2014 and 2015, and that Islamic State jihadist group used mustard gas in 2015.

The head of Russia's non-proliferation department, Mikhail Ulyanov, told UN member states last week that Russia will study the report on Khan Sheikhun by the JIM to "judge if it deserves the extension."

Source: AFP