Yemeni President Abd Rabbuh Mansour Hadi has vowed to restore state authority and warned of a "civil war" in the Sunni-majority country as Shia rebels were seen in almost total control of the capital, Sanaa.

"Sanaa is facing a conspiracy that will lead towards civil war," Hadi said in a speech at the presidential palace on Tuesday, two days after the rebels took control of all other key state institutions in the capital, overshadowing a UN-brokered peace deal.

"Many powers came together, either those who lost their interests in Yemen or those pushed by their personal grievances to take their revenge on their country rather than on individual, or the opportunistic who take advantage of any disaster to attack the country," said Hadi.

Al Jazeera's Mohamed Vall, reporting from Sanaa, said that the president's comments had created a lot of confusion in the country.

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"They don't know what he means. Is the conspiracy the fact that he was made to sign a deal that he didn't like to sign? Or conspiracy whether he now has second thoughts about the Houthi takeover and he sees it in it's real nature? He did not mention who is behind this conspiracy," said our correspondent.

Hundreds of rebel fighters manned checkpoints on the airport road and other major thoroughfares in the capital on Tuesday, while heavily armed patrols cruised the streets in four-wheel-drive vehicles, the AFP news agency reported.

'Sanaa will not fall'

Rebels were posted outside the public offices they entered on Sunday, which include the main government building, parliament, army headquarters and the central bank, alongside small detachments of military police.

Army accused of failing to protect Sanaa from Houthis

But Hadi insisted that "Sanaa will not fall."

UN envoy Jamal Benomar, who brokered Sunday's agreement 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.

As Benomar spoke, the peace accord seemed to be holding after a week of clashes between Shia rebels and Sunni fighters that the government said killed at least 200 people.

The Houthi rebels, who last year rebranded themselves as Ansarullah (Supporters of God), waged a decade-long insurgency in the mountainous north before launching a bid for power in Sanaa last month.

Also on Tuesday, Reuters news agency citing witnesses and a local official, reported that a drone similar to that used by the US to track down and attack suspected members of al-Qaeda in the Arabian Peninsula, crashed in the southern part of the country on Tuesday.

Witnesses said the aircraft crashed after it hit a mountain near the city of Beihan in the southern Yemeni Shabwa province.

A local official confirmed the aircraft crashed after it struck Shoab Mountain near Beihan and said that Yemeni troops and members of a local militia allied with the government quickly surrounded the area of the crash to keep onlookers away.

Source: Al Jazeera and agencies