EU foreign policy chief Federica Mogherini condemned as "unacceptable" recent attacks on civilian targets by the Syrian regime and ally Russia in northwest Syria.

"Recent attacks on a camp of internally displaced persons (IDPs) and the bombing of a critical life-saving health facility close to the Turkish border are yet another deplorable escalation in the deteriorating situation," a statement issued on Friday by Mogherini's office said.

"...indiscriminate attacks on critical civilian infrastructure, including health and education facilities, by the Syrian regime and its allies are unacceptable and must stop immediately," it added.

According to the Britain-based Syrian Observatory for Human Rights, at least 21 civilians including 10 children were killed on Wednesday in a bombardment by the regime of Syrian President Bashar al-Assad and Russia in Idlib province.

"The EU recalls that all parties to the Syrian conflict are bound to respect and uphold international humanitarian law and international human rights law. Equally, they are obliged to ensure unhindered humanitarian access to all people in need," the EU added.

Ruled by Syria's former Al-Qaeda affiliate since the start of the year, the Idlib region is one of the last parts of the country to escape the control of the Damascus government.

The region on Turkey's doorstep is home to some three million people, around half of whom have been displaced from other parts of the country by Syria's eight-year war.

It has repeatedly been the target of bombardment by the regime and its Russian ally, with the most recent spike in violence from May to August killing 1,000 civilians and displacing 400,000 people.

Many of those forced out of their homes fled north towards the Turkish border.