President Trump warned Russia, Syria and Iran on Thursday to stop killing innocent civilians in a military offensive against Syrian rebels.
The president said Syrian President Bashar al-Assad's forces, backed by Moscow and Tehran "are killing, or on the way to killing," thousands of innocent civilians in Idlib province.
"Don't do that!" Tweeted the president. "Turkey is working hard to prevent this massacre."
Syrian government forces advanced on Monday with a new military attack on the country's last rebel fortress, which began last week. The offensive has triggered a mass exodus of civilians fleeing to safer areas near the Turkish border.
Under the protection of air strikes and heavy bombing, Syrian troops have been pushing into northwestern Idlib province towards a large rebel-held city, Maaret al-Numan. The city is on an important road linking the capital Damascus with the northern city of Aleppo, Syria's largest.
The immediate goal of Assad's forces seemed to reopen the strategic road, closed by the rebels since 2012.
Idlib province is dominated by al Qaeda-linked militants. It is also home to 3 million civilians, and the United Nations has warned of the growing risk of a humanitarian catastrophe along the Turkish border.
Residents of towns and cities in southern Idlib province are fleeing with their belongings on trucks, cars and motorcycles.
The government's ground offensive resumed last week following the collapse of a ceasefire in force since late August.
• This story is based on wired service reports.