TRIPOLI (Reuters) - Rival armed factions battled for a second day on Friday in the worst outbreak of fighting in the Libyan capital Tripoli for more than a year.

Black smoke rose into the sky and explosions reverberated around the Abu Salim and Hadba districts, and a witness said a major road nearby had been blocked off with shipping containers.

Gunfire echoed across several other neighborhoods, only dying down towardsthe evening.

Tripoli is controlled by an array of armed groups which sporadically clash over territorial control or economic interests. Some groups have quasi-official status, but no government has succeeded in taming their power since the uprising that toppled Muammar Gaddafi five years ago.

The violence is the latest setback for the U.N.-backed Government of National Accord (GNA), which arrived in the capital in March with the acquiescence of some powerful armed factions but has struggled to assert its authority.

Late on Friday it issued a statement strongly condemning the clashes, calling for restraint, and saying it had instructed the Interior Ministry to take steps to protect public facilities and private property.

The GNA is part of Western efforts to end Libya’s chaos and unite factions aligned with two rival governments that were set up in Tripoli and eastern Libya in 2014. But the GNA has faced resistance from power brokers in eastern Libya and more recently from figures associated with a previous government in Tripoli that it had tried to displace.

Tripoli residents have become increasingly critical of the GNA as its leaders have failed to resolve severe economic problems, restore public services and improve security.

“The clashes between militias in Tripoli haven’t stopped and there’s no sign of the GNA,” one resident, Mohammed Salem, told Reuters on Friday. People in Tripoli had little idea about any political maneuvering behind the clashes, he said.

“What is going on in Tripoli is a war of power ... every militia badly wants to gain power because they know if they control the capital they rule,” Salem said.

U.N. Libya envoy Martin Kobler said he was “extremely alarmed” by the clashes. “We are in contact with the parties on the ground to urge an immediate end to this fighting.”

Sustained gunfire started on Thursday as armed groups mobilized military vehicles including tanks and pick-up trucks mounted with heavy weapons.

Overnight, a camp belonging to one brigade was bulldozed by a rival faction, according to videos posted on social media. There were unconfirmed reports that at least seven people had been killed. Some shops were shut and frightened residents rushed to stock up on provisions.

One of the capital’s bigger armed groups, the Tripoli Revolutionaries Brigade, said it had taken control of the Al Nasr Forest area around the Rixos hotel, where it said it had found dozens of explosive devices. A new legislative body linked to the GNA was ousted from the Rixos buildings in October.

Factional fighting in 2014 destroyed Tripoli’s international airport. The area around the city’s remaining airport, Mitiga, was calm on Friday and flights were operating.