KIEV (Reuters) - Rebels in eastern Ukraine refused to allow monitors from the Organization for Security and Cooperation in Europe to reach the encircled town of Debaltseve after a ceasefire took effect on Sunday, the head of the OSCE mission said.

The rebels have said the ceasefire does not apply to Debaltseve, scene of the worst fighting in recent weeks.

Organisation for Security and Cooperation in Europe mission chief Ertugrul Apakan said in an online briefing that the truce which began at midnight was largely being observed across eastern Ukraine. But he said Debaltseve and the rebel stronghold of Luhansk were exceptions where shooting continued.