Efforts are under way to try to negotiate the release of more than 220 Syrian Christians who were kidnapped last week by the Islamic State group, activists said.

Osama Edward, director of the Assyrian Network for Human Rights in Syria, and Younan Talia, a senior official in the Assyrian Democratic Organisation, said Sunni tribal sheikhs are trying to establish contact with IS.

Mr Talia said there had been no response yet from the militants.

IS fighters took the captives last week after sweeping through several villages in Syria's north-eastern Hassakeh province. The fate of those kidnapped, almost all of them Assyrian Christians, remains unclear.

The abductions have compounded fears among religious minorities in Syria and Iraq, where IS has repeatedly targeted minorities.