Yemenis inspect a vehicle on Tuesday destroyed during recent fighting between government troops and Shia rebels. 

AFP/Sanaa

President Abdrabuh Mansur Hadi warned on Tuesday of "civil war" in Sunni-majority Yemen and vowed to restore state authority as Shia 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.

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 Shia rebels and Sunni militiamen that the government said killed at least 200 people.

The Huthi rebels rebranded themselves last year as Ansarullah (Supporters of God).

Yemeni authorities have repeatedly accused Iran of backing the Huthi rebels, who also appear heavily influenced by Hezbollah, Lebanon's powerful Shia 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.

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.

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.

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