Russia said Tuesday it is talking to the United States about renewing the mandate of experts working to determine who was responsible for chemical weapons attacks in Syria, but the U.S. says Moscow won't consider the American draft resolution. Russia, which is Syria's most important ally, has submitted a rival draft resolution on renewing the experts' mandate to the Security Council. With two days left before Thursday's expiration of the mandate for the Joint Investigative Mechanism, known as the JIM, Russian Ambassador Vassily Nebenzia told The Associated Press that ''we are engaging with them. . We don't know whether we can come to an agreement.'' A spokesperson for the U.S. Mission to the United Nations said late Monday that ''Russia is mouthing words of support for JIM renewal, but those words are not backed up by any actions.'' ''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,'' said the spokesperson, who wasn't authorized to be quoted by name. ''The draft text Russia put forward without any negotiation is unhelpful, has no support, and cannot be taken seriously.'' Russia vetoed a U.S.-sponsored Security Council resolution on Oct. 24 that would have renewed the mandate of the experts from the U.N. and the Organization for the Prohibition of Chemical Weapons. Nebenzia said at the time that Moscow wanted to see a JIM report on attacks, which was issued two days later. When the JIM report was discussed in the council on Nov. 7, Russia clashed with the U.S. and other Western nations over its findings. The JIM's leaders said they were ''confident'' that Syria's government was responsible for an aerial attack on Khan Sheikhoun on April 4 using sarin that killed about 100 people and affected about 200 others who survived ''acute exposure'' to the nerve agent. The conclusion supported the initial findings by the United States, France and Britain, but Syria insists it has not used chemical weapons. The JIM experts also said they were ''confident'' the Islamic State extremist group was responsible for an attack at Um Hosh in Aleppo in September 2016 using mustard gas. Russia's deputy ambassador to the U.N., Vladimir Safronkov, dismissed the JIM's findings about Khan Sheikhoun as ''mythical or invented,'' asking how Syria could be blamed since investigators never visited the town or the air base where the sarin attack was claimed to have been launched. Nebenzia said Monday, ''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.'' U.S. Ambassador Nikki Haley told the Security Council last week that the Washington revised its resolution to include some points in the Russian draft. But she claimed the Russian draft would keep Syria from being investigated and said Russia is continuing ''to push unacceptable language only meant to undermine the investigators and divide this council.'' It remains to be seen whether the rival drafts can be reconciled and a way found to continue the JIM's work. Britain's U.N. ambassador told reporters Tuesday that it's extremely important that everyone who uses chemical weapons in Syria or elsewhere is held accountable, and the JIM is crucial in determining responsibility. ''Time is pressing, but I think everyone agrees that it should be renewed,'' Matthew Rycroft said, but the Russians ''have a different view about what sort of JIM.'' ''What is at stake is the professional, independent, objective, scientific, nonpartisan, depoliticized JIM which we've currently got, which we've had before, and which we need in the future,'' Rycroft said. In September 2013, Syria accepted a Russian proposal to relinquish its chemical weapons stockpile and join the Chemical Weapons Convention. That averted a U.S. military strike in response to an alleged chemical weapons attack that killed hundreds in the Damascus suburb of Ghouta.