Islamic State fighters tightened their grip on the historic city of Palmyra in Syria, days after capturing a provincial capital in neighbouring Iraq, hinting at the momentum of the group, which a monitor says holds half of Syrian territory.

Satellite images indicate that 290 cultural heritage sites in Syria, whose history stretches back to the dawn of civilisation, have been damaged by its ongoing civil war, the United Nations’ training and research arm (UNITAR) said.