After heavy aerial and land shelling, Syrian government forces managed to enter the northern and eastern neighbourhoods of Khan Sheikhoun as rebels withdrew from the area, according to the Britain-based Syrian Observatory for Human Rights (SOHR).

"This is a key victory for the regime forces," SOHR head Rami Abdel Rahman said.

Activists posted video footage on social media which showed dozens of shells falling on Khan Sheikhoun and wrote "regime forces follows a scorched earth policy to take control of towns and cities."

Earlier, three civilians were killed and 12 wounded in an attack on a Turkish military convoy in north-western Syria, according to the Turkish Defence Ministry.

"The Assad regime and its allies must return to the ceasefire in Idlib," US State Department spokeswoman Morgan Ortagus said in a tweet.

"Today's reckless airstrike on a Turkish convoy follows ongoing vicious attacks against civilians, humanitarian workers, and infrastructure," Ortagus added.

The violence in Idlib has shattered a truce deal reached in September between Russia and Turkey, a supporter of some rebel groups, to establish a demilitarized buffer zone in the Idlib enclave.

The surge in violence in the past few days in the southern countryside of Idlib has displaced 25,000 people, who fled to northern rural areas, the city of Idlib and areas close to the border with Turkey, the SOHR said.

Last month, the United Nations said the government's campaign to capture Idlib has displaced since April more than 400,000 people.

Australian Associated Press