* PM orders regular military to control armed groups
* Benghazi airport closed due to clashes
* Algeria sends special forces to evacuate envoys
(Adds airport closed, updates death tolll)
By Ayman al-Warfalli and Ahmed Elumami
BENGHAZI, Libya, May 16 Libyan irregular forces
backed by helicopters clashed with Islamist militias in Benghazi
on Friday in fighting that left at least 19 people dead and
posed a new test to the fragile government.
Members of the self-declared Libyan National Army, led by
retired General Khalifa Haftar, shelled bases belonging to Ansar
al-Sharia and another Islamist militant group in Benghazi, said
Mohamed Al-Hejazi, a spokesman for Haftar's forces.
The violence prompted Libya's prime minister to order the
regular military to control any armed groups - including
Haftar's forces - in the eastern city, where militants often
clash with the army, and assassinations and bombings are common.
Authorities closed the city's Benina airport in the evening
because of the clashes.
Since the 2011 civil war that ousted Muammar Gaddafi after
42 years of one-man rule, Libya has been unable to impose
authority over brigades of former rebels who refuse to disarm
and have carved out regional fiefdoms.
Highlighting the instability, Algeria sent a team of special
forces to evacuate its ambassador and embassy staff from Libya
in a military plane after a militant threat to its embassy,
officials and a security source said on Friday.
Benghazi, the cradle of the NATO-backed uprising against
Gaddafi, in particular has struggled to curb violence and stem
attacks blamed on Ansar al-Sharia, which often operates openly
despite being designated a terrorist organisation by Washington.
Prime Minister Abdullah al-Thinni told reporters: "We have
given orders ... to intercept any force trying to enter Benghazi
because they don't have legitimacy from the state."
Haftar, a leading figure in the anti-Gaddafi revolt, in
February stirred rumours of a coup by appearing in military
uniform to call for a presidential committee to be formed to
govern until new elections.
It was not clear how much support he commands, but it seems
likely his forces are drawn from the country's nascent army,
which is still in training. Tripoli's government said in
February he had no authority and threatened legal action.
Hejazi dismissed the government's rejection on Friday of the
legitimacy of Haftar's forces and said they were forcing
militants from their bases into the city because the government
had failed to help Benghazi.
"We're telling them we have the legitimacy from the
civilians who suffer on a daily basis from the killings
targeting the police and military," he said. "We are fighting
militias who threaten stability."
The city was calmer in the evening after the clashes in the
morning, when witnesses said at least one regular army
helicopter had been used in the assaults on the Islamist bases.
At least 19 people were killed and almost 70 injured in the
fighting, medical sources at local hospitals said.
Libya's government is fragile and the parliament almost
paralysed by rivalries, with little progress to full democracy
made since 2011. A planned new constitution is still unwritten
and the country is on its third prime minister since March.
U.S. and European countries are helping build up the regular
army but Libya's armed forces and government cannot control the
brigades of ex-rebels and militants who once fought Gaddafi.
The North African nation's vital oil export industry has
suffered badly and is often targeted by armed protesters seeking
a greater share of oil wealth, federalist power for the regions
or just better basic services.
Since last summer, armed protesters have repeatedly closed
down ports and oilfields, bringing production down to around
200,000 barrels per day from the 1.4 million bpd that the OPEC
member state produced before the protests erupted.
(Additional reporting by Ahmed Elumami; Writing by Patrick
Markey; Editing by Alison Williams)