Daesh militants sealed off the coastal route linking Noufliya and Ras Lanouf towns in eastern Sirte, entrapping those fleeing conflict there and forcing them to go back, a local source said.
The militants closed the road by containers, barbed wire and sand barricades, the source added.
The militants claimed that the closure is meant to block the advance of government forces towards Sirte.
Daesh took advantage of Libya's security vacuum and political turmoil to establish itself in Sirte last year. It controls a strip of coast about 250 km long around the city, but it has struggled to hold ground elsewhere in the country.