Libya's new army chief of staff on Monday declared "war on terrorists" as he was sworn into office after parliament selected him to tackle unrest sweeping the north African nation.
Abdel Razzak Nadhuri, promoted to general when he took up his new role, spoke as Libyan jihadist group Ansar al-Sharia urged other Islamists to unite under its banner.
Also on Monday, the interim General National Congress (GNC), officially replaced earlier this month by the new parliament, named a pro-Islamist figure to form a rival "salvation government", according to a television report.
"Allow me to declare, from this moment on, war on obscurantists, terrorists and takfiris (extremists)," said Nadhuri, whose predecessor General Abdessalam Jadallah al-Abidi was sacked by parliament.
Nadhuri, from the town of Marj, 1,100 km (600 miles) east of Tripoli, took up his post in the violence-plagued country as Libya's foreign minister and his counterparts from neighbouring states met in Cairo to discuss the Islamist threat.
Ansar al-Sharia, which Tripoli and Washington have both branded a "terrorist" organisation, urged other Islamists to beware what it dubbed Western plots aimed at "opposing the mujahedeen under the pretext that they are extremists".
"Unite with the mujahedeen in Benghazi so together we can defend the same objective -- a total rejection of any Western plan" for Libya, it said in an online message.
"Proclaim that your struggle is for sharia (Islamic law) and not democratic legitimacy, so the world unites under the same banner to bolster the forces of good against the forces of evil," it added.
Libya's new parliament, elected in June to replace the Islamist-dominated GNC, is openly opposed by the jihadists.
Meeting in Tobruk, 1,600 kilometres (1,000 miles) east of the capital to avoid the strife in Tripoli, parliament had grilled Abidi on August 10 on the army's inability to restore law and order to Tripoli and Benghazi, the country's two largest cities where militiamen have run rampant.
- Congress meets again -
"Colonel Abdel Razzak Nadhuri was chosen by 88 out of 124 MPs present and promoted to the rank of general," parliament spokesman Mohammed Toumi told AFP.
He added that Abidi had been sacked.
The outgoing GNC, responding to a weekend call from Islamists to resume business, met on Monday in Tripoli and began deliberations despite the lack of a quorum, local media reported.
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An-Nabaa television station, seen as close to the Islamists, said the GNC meeting opened with about 80 members present, though the quorum is 94.
The station said the GNC selected Omar al-Hassi to form a "salvation government", without saying how many members voted for the appointment.
A government headed by interim Prime Minister Abdullah al-Thani already exists and is operating like parliament in Tobruk.
Overnight Saturday-Sunday, parliament stated its intention to fight back against the Islamists, using the regular armed forces.
"The groups acting under the names of Fajr Libya and Ansar al-Sharia are terrorist groups and outlaws that are rising up against the legitimate powers," parliament charged in a statement.
Fajr Libya is a coalition of Islamist militias, mainly from Misrata, east of Tripoli. Ansar al-Sharia controls around 80 percent of the eastern city of Benghazi.
Ansar al-Sharia's appeal for jihadist unity came after Islamist militiamen from Misrata said they had seized Tripoli international airport from the nationalist militia from Zintan in the west, who had controlled it previously.
- Airport terminal gutted -
Footage broadcast on Monday showed the departures terminal ravaged by fire and around a dozen aircraft from Libyan companies bearing signs of damage caused by fighting.
The images appeared to confirm that the airport 30 kilometres (20 miles) south of Tripoli had fallen into Islamist hands.
The Islamist militias openly challenged parliament's legitimacy on Sunday after announcing their seizure of the airport, plunging Libya's rocky political transition into fresh crisis.
In Cairo, Egypt's Foreign Minister Sameh Shoukri warned Monday that a spillover of lawlessness from Libya could prompt foreign intervention, saying this should be avoided.
"We have felt the effects of the escalating Libyan situation on the security of neighbouring countries through the presence of extremist and terrorist elements which extended to other countries through arms dealing and trafficking," he said.
"This affects the sovereignty of neighbouring countries and threatens their stability. This could affect the interests of other countries outside the region and could lead to forms of intervention in Libyan affairs, which should be avoided."
Shoukri's Libyan counterpart, Mohamed Abdelaziz, said Tripoli awaited a UN Security Council resolution that would send a "strong message" to end the fighting in his country.