* Any drone use would signal more sophisticated warfare
* Shelling continues on Sunday in outskirts of capital
* Tripoli airport reopens (Adds airport reopens)
By Ulf Laessing and Hani Amara
TRIPOLI, April 21 (Reuters) - Explosions shook the Libyan capital Tripoli late on Saturday after an air strike, residents said, in an escalation of a two-week offensive by eastern forces on the city held by the internationally recognised government.
A Reuters reporter and several residents said they saw an aircraft circling for more than 10 minutes over the capital with a humming sound before opening fire on a southern suburb, scene of the heaviest fighting between the rival forces.
Reuters was unable to confirm whether an aircraft or unmanned drone was behind the strike which triggered heavy anti aircraft fire. Residents had reported drone strikes in the past days but there has been no confirmation and explosions heard in the city centre this time were louder than in previous days.
Residents counted several missile strikes which apparently hit a military camp of forces loyal to Tripoli in the Sabaa district. Authorities had closed Tripoli's only functioning airport but reopened it hours later, the airport's website said.
The Libyan National Army (LNA) force loyal to commander Khalifa Haftar started an offensive two weeks ago but has been unable to breach the government's southern defences.
If a drone strike was confirmed this would point to more sophisticated warfare. The LNA has so far mainly used ageing Soviet-made jets from the air force of Muammar Gaddafi, toppled in 2011, lacking precision firepower and helicopters, according to residents and military sources.
In the past the United Arab Emirates and Egypt have supported Haftar with air strikes during campaigns to take eastern Libya. Both countries flew air strikes on Tripoli in 2014 during a different conflict to help a Haftar-allied force, U.S. officials said at the time.
Since 2014 the UAE and Egypt have provided the LNA with military equipment such as aircraft and helicopters, helping Haftar to gain the upper hand in Libya's eight-year conflict, past U.N. reports have established.
The UAE even built an air base in Al Khadim in eastern Libya, one such report said in 2017.
The air strikes, which were also filmed by residents in video posted online, came after a day of heavy clashes in southern districts, with shelling audible in the city centre.
The violence spiked after the White House said on Friday that President Donald Trump spoke by with Haftar earlier in the week.
The disclosure of the call and a U.S. statement that it "recognized Field Marshal Haftar's significant role in fighting terrorism and securing Libya's oil resources" has boosted the commander's supporters and enraged his opponents.
Western powers and the Gulf have been divided over a push by Haftar's forces to seize Tripoli, undermining calls by the United Nations for a ceasefire.
Both sides claimed progress in southern Tripoli on Saturday, but no more details were immediately available.
A Reuters TV cameraman visiting the southern Khalat Furgan suburb on Saturday heard heavy shelling but saw no apparent change in the frontline. Shelling continued in the southern outskirts of the capital on Sunday.
On Friday, two children were killed in shelling in southern Tripoli, residents said. The fighting has killed 220 people and wounded 1,066, the World Heath organization (WHO) said.
It was unclear why the White House waited several days to announce Monday's phone call.
On Thursday, both the United States and Russia said they could not support a U.N. Security Council resolution calling for a ceasefire in Libya at this time.
Russia objects to the British-drafted resolution blaming Haftar for the latest flare-up in violence when his LNA advanced to the outskirts of Tripoli earlier this month, diplomats said.
The United States did not give a reason for its decision not to support the draft resolution, which would also call on countries with influence over the warring parties to ensure compliance and for unconditional humanitarian aid access in Libya. (Reporting by Ulf Laessing, Ahmed Elumami and Ayman al-Warfalli; Editing by William Maclean and Alison Williams)
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