Libya’s UN-backed prime minister has vowed to defend the capital Tripoli as forces loyal to a rival advance from the east.
In a televised address Fayez al-Serraj accused General Khalifa Haftar of launching a coup, saying his troops would be met with “strength and power”.
The rebels are on the outskirts of the capital and say they have seized Tripoli’s international airport.
Tripoli is the base of the UN-backed, internationally recognised government.
Rebel forces are advancing on Tripoli in a multi-pronged attack from the south and west of the city, although they have reportedly been slowed by pro-government fighters.
Gen Haftar’s Libyan National Army (LNA) troops seized the south of Libya and its oil fields earlier this year.
Libya has been torn by violence and political instability since long-time ruler Muammar Gaddafi was deposed and killed in 2011.
What’s happening in Libya?
Gen Haftar – who was appointed chief of the LNA under an earlier UN-backed administration – ordered his forces to advance on Tripoli on Thursday, as UN Secretary General Antonio Guterres was in the city to discuss the ongoing crisis.
Gen Haftar spoke to Mr Guterres in Benghazi on Friday, and reportedly told him that his operation would not stop until his troops had defeated “terrorism”.
Prime Minister al-Serraj said his government had “extended our hands towards peace” while Gen Haftar had declared a coup.
Forces have been ordered “to deal with the threat of those striving to destabilise and intimidate civilians”, he said, adding those responsible will be brought to justice.
Despite international demands to stop the advance, the LNA now says they have seized the disused international airport south of Tripoli and reportedly declared a no-fly zone over the west of the country, although the situation on the ground remains unclear.
The Libyan air force, which is nominally under government control, said it had targeted an area 50km (30 miles) south of the capital on Saturday morning with “intensive strikes”. The LNA vowed to retaliate.
Tripoli residents have begun stocking up on food and fuel, AFP reported.
What’s been the reaction?
The G7 group of major industrial nations has urged all parties “to immediately halt all military activity”. The UN Security council has issued a similar call.
Russia has also called on parties in the escalating conflict to find an agreement.
Speaking in Egypt, Russian foreign minister Sergei Lavrov warned against what he called foreign meddling in Libya, while Egypt’s foreign minister Sameh Shoukry said Libya’s problems could not be solved by military means.
Both countries have provided support to Gen Haftar.
UN envoy Ghassan Salame said on Saturday that a conference planned for 14-16 April intended to pave the way for elections would still be held.
Hope dashed for a political resolution?
By Sebastian Usher, BBC Arab affairs editor
It’s still unclear how much this is a show of force to bolster Gen Haftar’s position or a genuine effort to seize Tripoli.
He returned during the revolution and he’s subsequently become the most powerful military leader in a country rife with militias, allied to a rival government in the east.
Despite the chorus of international concern over his actions, he has had support from powerful outside players, including the UAE and Egypt.
Efforts towards a political resolution for Libya have foundered time after time. The most recent hopes may once again have been dashed.
Who is Khalifa Haftar?
Born in 1943, the former army officer helped Colonel Muammar Gaddafi seize power in 1969 before falling out with him and going into exile in the US. He returned in 2011 after the uprising against Gaddafi began and became a rebel commander.
In December Haftar met Prime Minister Fayez al-Serraj from the UN-backed government at a conference but refused to attend official talks.
He visited Saudi Arabia last week, where he met King Salman and Crown Prince Mohammed bin Salman for talks.