President Donald Trump on Thursday, Dec. 26, issued a warning to Russia, Syria, and Iran that are waging a military offensive to regain a rebel stronghold that relief groups said has displaced thousands of civilians.

“Russia, Syria, and Iran are killing, or on their way to killing, thousands of innocent civilians in Idlib Province,” President Trump tweeted. “Don’t do it! Turkey is working hard to stop this carnage.” 

Syrian government forces allied with Russia and Iran have stepped up air strikes in southern and eastern Idlib Province since late last month in an attempt to retake one of the last rebel-held territories in the country, according to The Associate Press. 

A Syrian relief group called the Syrian Response Coordination Group told The Associated Press that over 200,000 civilians had fled their homes amid a bombardment from Syrian government forces there, with many of them fleeing to the Turkish border. 

In a statement issued on Dec. 23, a spokesman for the United Nations secretary-general said the offensive has resulted in dozens of civilian casualties and the displacement of at least 30,000 civilians in the past week alone, and called for “an immediate cessation of hostilities” in the province while demanding “sustained, unimpeded and safe humanitarian access to civilians, including through the cross-border modality” for those fleeing.

Turkish President Recep Tayyip Erdogan earlier this week warned that Turkey, which already hosts some 3.7 million Syrian refugees, could not handle a new wave of refugees from Syria, reported the BBC.

“If the violence toward the people of Idlib does not stop, this number will increase even more. In that case, Turkey will not carry such a migrant burden on its own,” he said. “The negative effects of this pressure on us will be an issue felt by all European countries, especially Greece.”