An airstrike destroyed a makeshift clinic supported by an international aid group in northern Syria on Monday, killing and wounding several people, activists and aid officials said.

Mirella Hodeib of Doctors Without Borders - also known by its French acronym MSF - said the airstrike destroyed the MSF-supported structure in the north-western town of Maaret al-Numan in Idlib province.

She had no immediate word on casualties or the circumstances of the strike.

The British-based Syrian Observatory for Human Rights said Russian warplanes targeted the makeshift hospital, destroying it and killing nine people.

The Observatory, which tracks the casualties in Syria's five-year civil war, said dozens were also wounded in the airstrike.

Syrian troops have been on the offensive in northern Syria under the cover of Russian airstrikes over the past week.

The ground offensive has been focused on the northern province of Aleppo while Monday's airstrike struck the clinic in the nearby Idlib province.

"The entire building has collapsed on the ground," said opposition activist Yahya al-Sobeih, speaking by telephone from Maaret al-Numan.

He added that five people were killed near the clinic and "all members of the medical team inside are believed to be dead".

An aid official said at least one patient died and nine Syrian staffers were missing.

Casualty figures are often sketchy and conflicting, and cannot be independently verified because of the inaccessibility of the conflict zones.

Meanwhile in Brussels, European Union officials called on Turkey to halt its military action in Syria after Turkish forces shelled positions held by a US-backed Kurdish militia over the weekend.

The EU's foreign policy chief Federica Mogherini said that "only a few days ago, all of us including Turkey, sitting around the table decided steps to de-escalate and have a cessation of hostilities".

She said more fighting "is obviously not what we expect".