A Libyan jihadist group urged other Islamists to unite under its banner on Monday after parliament appointed a new army chief to tackle the unrest sweeping the North African nation.
Ansar al-Sharia, which Tripoli and Washington have both branded a "terrorist" organisation, made the call as Libya's foreign minister and his counterparts from neighbouring states met in Cairo to discuss the Islamist threat.
"Unite with the mujahedeen in Benghazi so together we can defend the same objective -- a total rejection of any Western plan" for Libya, Ansar al-Sharia said in an online message aimed at other militias in the violence-plagued country.
"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.
Ansar al-Sharia urged other Islamists to beware what it dubbed Western plots aimed at "opposing the mujahedeen under the pretext that they are extremists".
Libya's new parliament, elected in June to replace an Islamist-dominated General National Congress transitional political body, is openly opposed by the jihadists.
On Sunday, MPs appointed a new chief of staff to replace General Abdessalam Jadallah al-Abidi, who was grilled by parliament 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.
"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.
Parliament, which sits in Tobruk, 1,600 kilometres (1,000 miles) east of the capital, held Abidi responsible for the deteriorating security situation and blamed him for backing certain militias that in theory report to the army.
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.
"These two groups are a legitimate target of the national army, which we strongly support in its war to force them to halt their killings and hand over their arms".
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.
Footage broadcast on Monday by a television station close to the Islamists 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.