Libyan forces said on Friday they had edged further into the center of Sirte as they seek to recapture the city from Islamic State, following heavy fighting until late the previous evening that left dozens dead.

Forces aligned with Libya's United Nations-backed government in Tripoli advanced rapidly on the militant group's Libyan stronghold in May, but they have faced resistance from snipers, suicide bombers and mines as they have closed in on the city center.

Sirte had been controlled by Islamic State since last year, becoming its most important base outside Syria and Iraq, and its loss would be a major setback for the group.