Islamic State (IS) militants attacked a number of villages in a predominantly Christian area of northeastern Syria yesterday.

Heavy mortar attacks from IS began around dawn, local activists report, with counter attacks from Kurdish and Assyrian forces.

The Syrian Observatory for Human Rights reports that dozens were killed on both sides in the clashes.

The villages under siege, including Tel Nasri, Tel Mkhaz, Tel Mazas, Tel Ruqba, and Tel Hufyan, are situated on the Khabur river in al-Hasaka province.

Targeting these villages was part of a strategy to gain control of Tal Tamr, which has one of the major bridges across the river. It would mark a significant territorial gain for IS as it acts as a gateway to other areas already under their control in Iraq.

"If ISIS wants to go east toward the Iraqi border, the only corridor they have is that bridge [in Tal Tamr.] Of course, they don't mind cleaning the area of Assyrians while they're at it," Osama Edwards, the director of the Assyrian Network for Human Rights told the Wall Street Journal.

Last month more than 250 Assyrian Christians were kidnapped from the same area, though some of these have since been released.

Yesterday IS also destroyed the remains of the 2,000-year-old city of Hatra in northern Iraq. Hatra, which is a UN world heritage site, is about 70 miles from Mosul, the largest Iraqi city under IS control.

This latest attack follows the desecration of the artefacts in Mosul's museum a week ago, and on Thursday they attacked the remains of the Assyrian city of Nimrud.

"The destruction of Hatra marks a turning point in the appalling strategy of cultural cleansing under way in Iraq," Irina Bokova, head of the UN cultural agency UNESCO, told Reuters.