Libya's Islamist-dominated General National Congress on Monday threw down the gauntlet to the interim government of the near-lawless North African state by naming a prime minister-designate to form a rival administration.
The GNC, officially replaced earlier this month by a freshly-elected parliament, selected pro-Islamist Omar al-Hassi to form a "salvation government", a spokesman said.
"The GNC dismissed (interim premier) Abdullah al-Thani as head of government and gave Omar al-Hassi a week to form a salvation government," Omar Ahmidan said at a news conference in Tripoli, where GNC members met.
At the same time, Libya's new army chief declared "war on terrorists" after the elected parliament, holed up 16,000 kilometres (10,000 miles) from Tripoli in the eastern city of Tobruk, selected him to tackle unrest sweeping the nation.
"Allow me to declare, from this moment on, war on obscurantists, terrorists and takfiris (extremists)," said Abdel Razzak Nadhuri, promoted to general on taking up his new role.
The GNC meeting, for its part, gave its support for "legitimate moves aimed at liberating the country," Ahmidan said, referring to the weekend capture of Tripoli international airport by the Fajr Libya (Libyan Dawn) Islamist coalition.
The GNC, whose re-emergence plunges Libya's rocky political transition into fresh crisis, met following a request from Islamists, who accused parliament in Tobruk of complicity in raids last week by mystery warplanes on Islamist positions near the airport.
Thani rejected the GNC's motions, saying its decisions were illegal.
"The meeting was illegal, its decisions are illegal and the only legislative body is parliament," Thani said in a televised news conference from Tobruk.
He said Islamist militants had ransacked and set fire to his house in Tripoli.
"The homes of many Libyans have suffered the same fate," Thani said, blaming Fajr Libya fighters.
The whole of Tripoli is unsafe and the government headquarters building has been threatened, he added.
Telling of "threats, thefts and looting" in the capital, Thani said "no public service can operate in these conditions.
"Libya cannot be ruled by force of arms. Only the police and army should have weapons," the premier said.
Parliamentary speaker Aguila Salah Issa told the news conference he will go to Egypt on Tuesday for talks with President Abdel Fattah al-Sisi
The swearing-in of new chief of staff Nadhuri came as Libya's foreign minister and his counterparts from neighbouring states met in Cairo to discuss the Islamist threat.
The neighbours backed an Egyptian call for Libya's rival militias to be disarmed, while agreeing with Cairo that there should be no foreign intervention to stem spiralling lawlessness.
Libyan jihadist group Ansar al-Sharia on Monday urged other Islamists to unite under its banner.
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 parliament, elected in June, and Thani's government decamped to Tobruk after the army proved unable to restore law and order to Tripoli and Benghazi, the country's two largest cities.
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 Fajr Libya said they had seized Tripoli airport from the nationalist militia of Zintan in the west, who had controlled it since the overthrow in 2011 of long-time dictator Moamer Kadhafi.
Footage broadcast on Monday showed the departures terminal ravaged by fire and around a dozen aircraft from Libyan companies damaged in the 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.