The United States on Wednesday was headed for a showdown at the United Nations with Russia over prolonging the mandate of an investigative panel looking into who is responsible for chemical weapons attacks in Syria.
The joint UN-OPCW probe is set to present its final report on October 26 on who was behind the sarin gas attack in Khan Sheikhun, just weeks before its mandate expires.
Russia, a key ally of Syrian President Bashar al-Assad, has said that it wants to study the report on Khan Sheikhun before deciding whether to support another one-year mandate for the panel.
US Ambassador Nikki Haley said the Security Council must vote on renewing the panel, known as the Joint Investigative Mechanism (JIM), before the report is released.
"The Russians have made it very clear that should the report blame the Syrians suddenly they won't have faith in JIM. If the report doesn't blame the Syrians, then they say that they will," Haley told reporters.
"We can't work like that."
The United States will circulate a draft resolution on Wednesday aimed at extending the JIM and will seek a vote at the Security Council "as soon as possible," Haley said.
Russia could decide to use its veto to block the draft resolution and effectively shut down the investigation of deadly gas attacks in Syria.
"It would be a shame if Russia chose to decide whether to have an investigative mechanism based on who is to blame in Khan Sheikhun," said Haley.
The United States, France and Britain have accused Assad's forces of carrying out the April 4 attack on Khan Sheikhun, an opposition-held village in Idlib province.
At least 87 people, including more than 30 children, died in the attack that drew global outrage over the use of banned sarin as a weapon.
During a briefing last week to UN member-states, Russian foreign ministry official Mikhail Ulyanov said the sarin attack was most likely caused by a bomb set off directly on the ground and not by a Syrian air strike.
Russia will study the report on Khan Sheikhun by the JIM to "judge if it deserves the extension," said Ulyanov.
Haley said there was "overwhelming support" in the council to allow the JIM to continue its work and stressed that "we can't go and pick and choose who we want to be at fault and who we don't."
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 jihadists used mustard gas in 2015.
The Organisation for the Prohibition of Chemical Weapons (OPCW) earlier this year presented a report confirming sarin gas was used in Khan Sheikhun, but did not assign blame, leaving that determination to the JIM.
In total, the OPCW is investigating as many as 45 suspected chemical attacks in Syria since mid-2016 including the recently-disclosed use of sarin on an opposition-held village on March 30.
Those investigations are then sent to the JIM which seeks to determine who is responsible for the attacks.