President Abdrabuh Mansur Hadi warned Tuesday of "civil war" in Sunni-majority Yemen and vowed to restore state authority as Shiite rebels appeared to be in near-total control of the capital.
"Sanaa is facing a conspiracy that will lead towards civil war," Hadi said in a speech at the presidential palace, two days after the rebels took control of all other key state institutions in the city, overshadowing a UN-brokered peace deal.
Hundreds of rebel fighters manned checkpoints on the airport road and other major throughfares on Tuesday while heavily armed patrols cruised the streets in four-wheel-drive vehicles, AFP correspondents reported.
Insurgents alongside small detachments of military police stood guard outside public offices they entered on Sunday, which include the main government building, parliament, army headquarters and the central bank.
But Hadi insisted: "Sanaa will not fall."
UN envoy Jamal Benomar, who mediated the accord aimed at ending deadly fighting between the rebels and Sunni Islamists, said the rebels' taking of key institutions virtually without resistance seemed to signify the "collapse" of the security forces in Sanaa.
"What has happened these past few days could lead to the collapse of the Yemeni state and the end of the political transition," he told Al-Arabiya television late Monday.
As Benomar spoke, the peace accord seemed to be holding after a week of clashes between Shiite rebels and Sunni militiamen that the government said killed at least 200 people.
The Huthi rebels, who last year rebranded themselves as Ansarullah (Supporters of God), claim direct descent from the family of the Prophet Mohammed.
Yemeni authorities have repeatedly accused Iran of backing the Huthi rebels, who also appear heavily influenced by Hezbollah, Lebanon's powerful Shiite militia that is backed by Tehran.
Ansarullah waged a decade-long insurgency in the mountainous north before launching a bid for power in Sanaa last month.
- Trying to rescue transition -
Sunday's UN-brokered deal, signed by Hadi and the main political parties, aims to put the troubled transition back on track in impoverished Yemen, which borders oil kingpin Saudi Arabia and is a key US ally in the fight against Al-Qaeda.
The speed of the rebel advance reflected the fragility of Yemen's regime three years after a deadly uprising forced veteran strongman Ali Abdullah Saleh from power.
Saleh was himself a Zaidi Shiite, a community which forms 30 percent of Yemen's mostly Sunni population but is the majority in the northern highlands, including Sanaa province.
Under Sunday's deal, Hadi had three days to bring a rebel representative into government as an adviser and to name a neutral replacement for prime minister Mohamed Basindawa.
Before the deal was struck, Basindawa tendered his resignation as the security forces surrendered state institutions without a fight, although it has yet to be formally accepted by the president.
A security protocol to Sunday's agreement requires the rebels to hand over the institutions they have seized, and once a new premier has been named, to start dismantling armed protest camps they established in and around Sanaa last month.
Rebel representatives refused to sign the security protocol at Sunday's ceremony, however.
Rebel spokesman Mohammed Abdessalam said they would do so only once the security forces had apologised for the deaths of rebel protesters during an attempt to storm government headquarters earlier this month.
The deal also requires Hadi to appoint an adviser from the separatist Southern Movement which has been campaigning for the secession of the formerly independent south.
The southerners' boycott of Hadi's UN-backed plans for the transition has been another major obstacle.
Southern grievances have allowed parts of the region to become strongholds for Al-Qaeda in the Arabian Peninsula (AQAP), regarded by Washington as the jihadist network's most dangerous arm.