(Raises casualty toll, adds detail from hospital spokesman)

TRIPOLI May 6 (Reuters) - Islamic State militants staged attacks on Thursday between their Libyan stronghold of Sirte and the city of Misrata, killing five people, officials said.

The jihadist group said it had taken control of several villages in the area following attacks on checkpoints, though reports that local security forces had retreated could not immediately be confirmed.

Islamic State 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 (155 miles) long around the city, but it has struggled to hold ground elsewhere in the country.

The West is hoping a U.N.-backed government that arrived in Tripoli at the end of March will be able to unite Libya's armed factions to take on Islamic State. But efforts to counter the group have so far depended on loose alliances of armed brigades that supported rival governments in Tripoli and the east.

Aziz Issa, the spokesman for Misrata central hospital, said three members of the local security forces had been killed in an attack on a checkpoint at Abu Grain, about 140 km (85 miles) west of Sirte.

He said about 40 people had been wounded in the attack and clashes that followed, and that they were still being brought to the hospital late on Thursday.

Separately, militants carried out a bomb attack in Baghla, to the south, a local official and a resident said. The official, from the nearby town of Bani Walid, said two residents were killed in the bombing.

Islamic State said in statement that its fighters had gained control over several villages in the area, including Baghla, Zamzam, and Abu Najaym, as well as the town of Abu Grain.

The group's militants regularly venture across the main road leading south from Misrata, and have carried out raids and attacks in the area before, including against checkpoints manned by brigades from Misrata.

The attacks on Thursday came as military forces in eastern Libya said they were preparing for a campaign to recapture Sirte.

There have also been reports that Misrata brigades were mobilising to advance against Islamic State, and pictures posted on social media last week showed convoys of dozens of vehicles on the road south from Misrata.

The U.N.-backed unity government has urged armed factions to hold back from attacking Sirte until it creates a unified military command. (Reporting by Ahmed Elumami and Ayman al-Warfalli; Writing by Aidan Lewis; Editing by Dominic Evans and Toby Chopra)