UNITED NATIONS: UN Secretary-General Antonio Guterres warned Wednesday that full-scale military operations in Syria’s Idlib province could lead to a “humanitarian catastrophe” and cautioned against the use of chemical weapons. Guterres’s warning came amid fears the Syrian government is mobilizing for a military offensive to retake Idlib, the last province still held by the country’s beleaguered rebels. “The Secretary-General is deeply concerned about the growing risks of a humanitarian catastrophe in the event of a full-scale military operation in Idlib province in Syria,” a UN statement said. “The Secretary-General once again reaffirms that any use of chemical weapons is totally unacceptable.” NATO warned on Wednesday that the Russian navy is building up its presence in the Mediterranean Sea amid growing tensions over the war in Syria. Russian Foreign Minister Sergei Lavrov on Wednesday described militants in Idlib as a “festering abscess” that needed to be liquidated. Speaking after talks with his Saudi counterpart Adel bin Ahmed Al-Jubeir in Moscow, Lavrov said militants were using civilians as a human shield. Lavrov told reporters that there was a political understanding between Turkey and Russia on the need to distinguish between the Syrian opposition and people he described as terrorists in Idlib Province. Guterres appealed urgently to the Syrian government and all other parties “to exercise restraint and to prioritize the protection of civilians.” Guterres also urged the guarantors of a so-called Astana peace initiative led by Turkey, Iran and Russia to step up their efforts “to find a peaceful solution to the situation in Idlib, the last remaining de-escalation zone.” According to western estimates, some three million people are at risk in the province, which borders Turkey. An offensive by the Syrian government, which wants to retake the province with the backing of Moscow, would have explosive repercussions for civilians as well as for moderate rebels and radical Islamists. During closed-door talks at the UN Tuesday that were requested by Russia, Moscow claimed, without evidence, that “white helmet” rescue workers were preparing a chemical attack in Idlib, according to diplomats, who called the allegations “very bizarre.” Western powers view those claims as an attempt to deflect attention from preparations for a Syrian military offensive. According to the diplomats, western powers have given the UN Security Council the names of Syrian commanders and regiments involved in the preparations for an offensive in Idlib, who could be held responsible in the event of attacks on civilians. During a public session on Syria at the UN Tuesday, Russia denied any possibility of a chemical attack in Idlib by the Syrian government. Russia’s Ambassador Vassily Nevenzia insisted that the Syrian military has no chemical weapons and did not intend to use any. Russia has provided crucial military support for Syrian government forces, which are expected to mount an offensive in the northern Idlib province, the last major rebel stronghold in the country. “We will not speculate on the intention of the Russian fleet, but it is important that all actors in the region exercise restraint and refrain from worsening an already disastrous humanitarian situation in Syria,” NATO’s chief spokeswoman, Oana Lungescu, said Wednesday. She says several of the Russian ships are equipped with cruise missiles. Russian defense officials could not be reached for comment. At least eight ships, including a missile cruiser and two missile-carrying submarines, have joined the Russian flotilla over the past three weeks. Russian media reports indicate there are around 15 Russian navy vessels in the Mediterranean overall. Moscow has repeatedly alleged that Syrian rebels are preparing a chemical weapons attack in Idlib as a provocation to bring a Western attack on Syrian forces. The newspaper Moskovsky Komsomolets said the naval buildup was connected to that prospect. “The United States and its allies have forced Russia to send a powerful sailing group to the Mediterranean,” it wrote on Tuesday. Western countries and independent analysts say Syrian government forces have carried out a number of chemical attacks over the course of the seven-year civil war. The US has vowed to respond if Syrian forces use chemical weapons in Idlib. Western countries carried out strikes on Syrian government forces after an alleged chemical attack earlier this year. Both Syria and Russia deny that government forces have ever used chemical arms.