The new U.S. envoy for Syria has issued a stark warning that Syrian government forces are preparing to use chemical weapons in Idlib, the last major rebel-held area of the country, which has been heavily bombed by Russian planes ahead of an expected offensive. Jim Jeffrey said: “I am very sure that we have very, very good grounds to be making these warnings. Any offensive is to us objectionable as a reckless escalation. There is lots of evidence that chemical weapons are being prepared.” Despite Syrian denials, experts from the U.N. and the Organization for the Prohibition of Chemical Weapons have said they are confident Syrian government forces were behind a Sarin attack in April 2017 that killed more than 80 people. U.N. officials say as many as 800,000 people could be displaced by fighting in Idlib. Turkey’s president, Recep Tayyip Erdoğan, is reportedly pressing Russia to order the Syrian government to back off from an assault on the enclave, fearing mass displacement of Syrian refugees into Turkey.