TRIPOLI, Aug 28 (Reuters) - A member of the leadership of Libya's U.N.-backed government who is close to powerful rival factions in the east of the country has said he will end his boycott of the Tripoli-based body.

The decision by Ali Gatrani could strengthen the Government of National Accord (GNA), coming days after a second boycotting member of the government's nine-member leadership, or Presidential Council, said he would resume his role.

But in a statement late on Saturday, Gatrani referred anew to concerns around the continuing power of armed groups in the politics of the oil-producing North African state.

Eastern factions have blocked the parliament based in the east from approving the GNA, saying they believe the U.N.-backed government is dependent on militias and is undermining eastern forces led by General Khalifa Haftar.

Western states are counting on the GNA as the best option in tackling the political chaos, security vacuum and economic collapse that have convulsed Libya since Muammar Gaddafi was toppled in an uprising five years ago.

The result of a U.N.-mediated deal signed in December, the GNA arrived in Tripoli, the capital in the west of Libya, three months later where it has gradually moved to install ministers.

But it has failed to win endorsement from the pre-existing parliament in the east, which is seen as indispensable if it is to extend its authority across the country.

Last week, the Council said it would resubmit a list of ministers to the parliament in the east, after some lawmakers there voted for a second time to reject it.

Gatrani said he was resuming his role in response to an invitation to a meeting on Sunday from Fayez Seraj, who heads both the GNA and the Presidential Council.

He said his top concern was "the rights of the Barqa region and its people ... whom we represent, along with their sons' sacrifices in the police and the army". Barqa is the name for Libya's eastern region.

Gatrani said he had been surprised by the Presidential Council's move from Tunis to Tripoli in March, even though the U.N. backed deal "states that the venue of Presidential Council meetings would be in the capital, Tripoli, only after the militias have left".

"For that we inform you that we are not going to respond to the call to convene unless the meeting venue is in a Libyan city controlled by regular police and army," he said.

The parliament now in the east left Tripoli in 2014 after armed opponents seized the capital and installed rival institutions there. The GNA has largely displaced the former government in Tripoli, but has struggled to win popular support.



(Reporting by Ahmed Elumami; writing by Aidan Lewis; editing by Mark Heinrich) ((Aidan.Lewis@thomsonreuters.com ; +216-29850352;))