US President Donald Trump warned on Monday the Syrian regime against launching an offensive against the northwestern province of Idlib. Regime leader Bashar Assad “must not recklessly attack Idlib Province. The Russians and Iranians would be making a grave humanitarian mistake to take part in this potential human tragedy," Trump tweeted. Regime forces and their allies have been amassing around the opposition-held region for weeks. "Hundreds of thousands of people could be killed. Dont let that happen!” added Trump. The United Nations and aid groups have warned that a full assault on Idlib could spark a humanitarian catastrophe on a scale not yet seen in Syrias seven-year-old conflict. A major offensive in Idlib, where displaced people make up nearly half of the population of 3 million, risks forcing another 700,000 Syrians from their homes, the UN has stated. It has called for humanitarian corridors to evacuate civilians. US Secretary of State Mike Pompeo on Friday said Washington views any regime assault on Idlib as an escalation of the war. Moreover, the State Department warned that Washington would respond to any chemical attack by Damascus. Nikki Haley, the US ambassador to the UN, wrote on Twitter late on Monday: “All eyes on the actions of Assad, Russia, and Iran in Idlib. #NoChemicalWeapons.”