TRIPOLI, May 26 (Reuters) - Heavy clashes between rival factions erupted in the Libyan capital Tripoli on Friday, with loud explosions and heavy artillery fire heard since the early morning.
The fighting appeared to be caused by a push to regain territory by armed groups linked to a self-declared, Islamist- leaning "national salvation government" that was set up in 2014.
It has been largely displaced by the U.N.-backed Government of National Accord (GNA) that arrived in Tripoli last year, but continues draw on armed support, especially from the western city of Misrata.
The GNA has struggled to exert its authority in Tripoli and beyond, or rein in the militias that have held power on the ground in Libya since the country's 2011 uprising.
A third government based in eastern Libya and aligned with military commander Khalifa Haftar has rejected the GNA.
The clashes follow a period of relative calm in Tripoli since March, when armed groups aligned with the GNA pushed rival factions back from central neighbourhoods.
There have been rumours for weeks that a counter-attack was being planned under the name "Libya Pride", which in Arabic is a play on "Libya Dawn", the coalition of militias that brought the salvation government to power in Tripoli three years ago.
A Libya Pride Facebook page with 17,000 followers carried a post overnight announcing: "With Allah, we officially launch the operation of southern Tripoli."
A rival faction aligned with the GNA said that "ideological gangs" had begun an attack "aiming to control the capital and put the country into a storm of violation and destabilisation, in addition to increasing the suffering of citizens in the holy month of Ramadan". The group said five of its men had been killed in the violence, and an unspecified number wounded.
The fighting was concentrated in the Abu Salim, Salahedeen and Qasr Bin Ghashir districts. Large plumes of black smoke could be seen billowing above the city's skyline. Shooting continued throughout Friday prayers.
"We have received calls from families who want to get out but unfortunately we can't reach them because of the clashes," one aid worker told Reuters.
A Reuters reporter saw tanks, armoured vehicles and pick-ups mounted with anti-aircraft guns driving towards the battle from the north of the city.
Pictures posted on the internet also showed firemen trying to extinguish a blaze in an office building in central Tripoli belonging to Mellitah Oil and Gas, a joint venture between Libya's National Oil Corporation and Italy's Eni.
U.N. Libya envoy Martin Kobler condemned the violence in a statement and called for an immediate restoration of calm. (Writing by Aidan Lewis; Editing by Tom Heneghan)