The United States and Britain have accused Russia of "denying the truth" as Moscow sought to rip up a report blaming Syria for a deadly chemical attack in April.
Russia said on Monday it was talking to the United States about the UN Security Council renewing an international inquiry into chemical weapons attacks in Syria, but Washington countered that Moscow had refused to engage on a US-drafted resolution.
The mandate for the joint inquiry by the UN and the Organisation for the Prohibition of Chemical Weapons (OPCW), which has found the Syrian government used the banned nerve agent sarin in an April 4 attack, expires on Friday.
Russia vetoed an initial US bid to renew the joint investigation on Oct 24, saying it wanted to wait for the release of the latest investigation's report two days later. It has since proposed its own rival draft resolution.
"We are talking to the US, it's not over yet," Russian UN Ambassador Vassily Nebenzia told reporters on Monday.
Last month, a report by a joint UN-OPCW panel said the Syrian air force on April 4 dropped a bomb on the opposition-held town of Khan Shaykhun, releasing the deadly nerve agent that killed more than 80 people, including children. The Syrian government has denied using chemical weapons.
"Russia has refused to engage on our draft resolution – which the vast majority of council members agree is the most viable text – in spite of our multiple attempts to consider Russian concerns," a spokesman for the US mission to the United Nations said on Monday.
A resolution needs nine votes in favour and no vetoes by Russia, China, the United States, Britain and France to pass. The council unanimously created the inquiry, known as the Joint Investigative Mechanism (JIM), in 2015 and renewed it in 2016.
But Russia has dismissed the Joint Investigative Mechanism (JIM) report, saying the experts did not travel to Khan Shaykhun and worked with samples Moscow maintains may have been tampered with by Western intelligence.
It is important that the JIM is renewed but on an updated mandate because the systemic errors that we saw with the recent report should be corrected and that's the aim of our resolution," Nebenzia said.
He added that if the mandate of the inquiry was not renewed, "It may send a bad signal, but the way the investigation has been conducted sends an even worse signal."
The JIM previously found that Syrian government forces were responsible for three chlorine gas attacks in 2014 and 2015 and that Daesh militants used mustard gas.
"The draft text Russia put forward without any negotiation is unhelpful, has no support, and cannot be taken seriously," said the spokesman for the US mission.
Syria agreed to destroy its chemical weapons in 2013 under a deal brokered by Russia and the United States.
The dispute has intensified after Russia and Iran, the Syrian regime's allies, proposed a resolution at the OPCW meeting last Wednesday which diplomats say effectively asks investigators to scrap the first probe into the Khan Shaykhun incident and launch a new investigation.
The draft resolution "decides to renew the work by the FFM on the incident with the use of chemical weapons in Khan Shaykhun in order to ensure a full-scale, professional and high-quality investigation to identify sarin," according to a copy seen by AFP.
"We are not turning back the clock," Russian ambassador Shulgin said.
"What we are asking for is to set up the clock in such a way that it ticks in rhythm with high standards of the chemical weapons prohibition convention," he said.
Britain's permanent representative to the OPCW, Peter Wilson, said London and other Western countries stood behind the original report and accused Moscow of wanting "to confuse the delegates of the OPCW."
The investigators "have not taken any evidence they can't corroborate from at least three sources," Wilson told AFP.
Earlier in his statement to the OPCW's Executive Council meeting – of which Russia and the United States are also members – Wilson accused Russia and Iran of "seeking to politicise" the OPCW.
"It is a thinly veiled political attack on the professional integrity" of the OPCW's director general Ahmet Uzumcu aimed at undermining the organisation's technical capability and competence, Wilson said.
Canada also joined the fray, saying that Syria, which joined the Chemical Weapons Convention in 2013 under joint US-Russia pressure, "forfeited the rights and privileges of membership, and should no longer be permitted to sit among us."