The United Nations closed its offices in the Yemeni capital on Thursday over fears of possible car bomb attacks, although Western embassies remained open.
Despite official denials of an alert, most shops in Sanaa were shuttered and little traffic ventured out onto the streets as rumours swirled among the city's residents of the risk of an imminent attack.
The American and Turkish schools were also closed.
Security forces have been on high alert in the capital since a brazen daylight attack on the defence ministry's sprawling headquarters on December 5 killed 56 people, among them expatriate medical staff.
Information gleaned during the investigation into that attack, which was claimed by Al-Qaeda, led to the discovery of two cars packed with explosives and a massive search for five more suspected to be still inside Sanaa.
"I drive around the city with fear that a blast could take place on any corner of the road. I'm afraid of dying in an attack," said Ibrahim Tayyar, one of the few taxi drivers working on Thursday.
State television on Wednesday aired horrific images of the defence ministry assault, taken from surveillance cameras, showing the assailants executing civilians and medics in cold blood.
The images show a car packed with explosives detonated at the gate to the complex, sending soldiers, medics and civilians gathered inside the compound running for cover.
After the blast, heavily armed militants dressed in combat fatigues are seen wandering through the corridors of the complex, shooting anyone they see, including a wounded female nurse who appears to be looking for help.
Another gunman in military uniform calmly approaches a group of people huddled in a corridor after the initial blast, before pulling a hand grenade from his jacket and hurling it at them.
The group dive for cover, before the grenade explodes and smoke blocks the screen.
Elsewhere in the complex, a doctor is seen running to rescue a wounded man before one of the attackers shoots both dead.
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"I did not get a wink of sleep all night. I've opened my shop but I'm afraid," said Qassem al-Baadani, a businessman who did not send his children to school out of fear.
A UN source said Wednesday that a warning from Yemeni authorities of a possible attack in Hada, the south Sanaa neighbourhood where UN offices are located, had triggered the closure order.
"Staff of the UN mission and UN agencies have received instructions not to turn up for work on Thursday," the source said.
The source said it was a "precautionary measure".
Yemen denounces 'smear campaign'
But a senior Yemeni security official said no warning had been issued through authorised channels and dismissed the alleged advice to the UN as part of "a campaign of rumours aimed at spreading fear in the country."
"Western embassy security chiefs met with Yemeni officials on Wednesday and no attack warnings were issued," the official told AFP, on condition of anonymity.
An adviser to Yemen's prime minister, Rajih Badi, denounced what he said was a "smear campaign launched by media supporting former president Ali Abdullah Saleh", accused by his opponents of trying to hinder the political transition since he was forced out of power last year.
Those behind the campaign are "seeking to sow panic among the population and to hinder the investigation into the (December 5) attack," he said, adding that no foreign embassies were closed on Thursday.
The US embassy confirmed it remained open and referred all questions about security to the Yemeni government. The British and French embassies were also operating normally.
UN special envoy Jamal Benomar has said the attack on the defence ministry should not be allowed to disrupt the transition from Saleh's 33-year rule.
In August, a security alert originating in Yemen prompted an unprecedented closure of American embassies across and beyond the Middle East, which was mirrored by the British and French missions in Sanaa.