Officials said that women and children were in two of the buildings in the city's Ghiza Bahriya district and that a small number of militants were still in the area.
Libyan forces, backed by U.S. air strikes, said on Monday they had gained control over the district on Monday after most of the militants still in the area were killed or captured.
Islamic State has been holding out for weeks in the district, close to Sirte's Mediterranean sea front, at the end of a grueling battle for Sirte that began in May.
Dozens of women and children, some of them migrants from sub-Saharan Africa held captive held by Islamic State, had escaped or had been released over recent days, allowing Libyan forces to move forward.
Ibrahim Irfaida, a top field commander, said late on Monday there were up to 10 houses in Ghiza Bahriya that had yet to be secured and five more that had been destroyed by air strikes but had been not yet checked.
"There are still some women and children and Islamic State fighters' bodies in those houses that we have not yet secured," he told Misrata FM radio. Another official, who asked not to be named, said some militants were still hiding in the buildings.
Irfaida said that even once Ghiza Bahriya was fully under control, Libyan forces would need to try to secure villages and valleys south of Sirte where militants have been active.
Libyan and Western officials say some Islamic State fighters escaped from Sirte in the early stages of the battle in order to wage an insurgent campaign from outside the city and there have already been attacks behind the front line.
Islamic State took over Sirte in early 2015, turning it into their most important base outside the Middle East and recruiting large numbers of foreign fighters.
Forces led by fighters from Misrata counter-attacked in May after jihadists moved along the coast towards the city. The brigades, nominally aligned with a U.N.-backed government in Tripoli, advanced rapidly towards the center of Sirte before suicide bombers, snipers and mines largely halted their progress.
Since Aug. 1, the United States has carried out more than 490 air strikes in support of the Misrata-led forces.
