The government quickly said it suspected al—Qaeda as behind the bombing on day in Aden’s free—trade zone, which went off after anti—government demonstrators in the city and across the nation again held large weekend rallies in their four—month campaign to oust Yemen’s autocratic leader of nearly 33 years.

A car bomb believed to have been set off by a suicide attacker killed three Yemeni security personnel in the southern city of Aden, the government said, as residents grew fearful of a possible attempt by Islamic militants to seize control of the strategic port city.

The government quickly said it suspected al—Qaeda as behind the bombing on day in Aden’s free—trade zone, which went off after anti—government demonstrators in the city and across the nation again held large weekend rallies in their four—month campaign to oust Yemen’s autocratic leader of nearly 33 years.

Regime opponents have accused the government of exaggerating the al—Qaed threat to try to hang on to Western support, and local investigators in Aden said it was too early to tell what caused Friday’s blast.

The months of political turmoil have raised fears, perhaps most acutely in the U.S., that Yemen’s al—Qaeda franchise will seize the opportunity and carve out more room to operate freely and plot attacks on the West from its redoubts in the country’s remote and mountainous hinterlands.

Residents of Aden said their worries of a possible militant takeover were fuelled by the sudden and unexplained withdrawal of military forces loyal to embattled President Ali Abdullah Saleh from checkpoints at the entrances to the city and other key positions. A similar government withdrawal preceded the recent takeover of two nearby towns by hundreds of Islamic militants, some of them thought to be linked to al—Qaeda in the Arabian Peninsula.

“We are all very worried of what lies ahead. There are rumours all over the town that militants from al—Qaeda will take over Aden,” said Mohammed al—Dalei, a 28—year—old teacher.

Some residents of Aden said gunmen appeared around the city in recent days, sometimes firing randomly in the air or at strategic buildings, such as the Central Bank.

A takeover of Aden would put extremist fighters in control of a major port at the southern entrance to the Red Sea and the vital shipping lane to and from the Suez Canal.

Friday’s explosion was heard throughout the city and blew out the glass facade of a four—storey building. Besides the three killed, three others were injured, said a medical and a security official who spoke on condition of anonymity because they were not authorized to talk to journalists.

Yemen’s president is clinging to power despite the daily protests against him and an attack on his palace this month that badly wounded him and forced him to fly to Saudi Arabia for medical treatment.

The crisis began in February with protests by largely peaceful crowds calling for Mr. Saleh to end his rule over the impoverished country on the southern edge of Arabia. A government crackdown on unarmed protesters has killed at least 167 people, according to Human Rights Watch.

The U.N.’s human rights office said on Friday it plans to send a team of investigators on a 10—day visit to Yemen starting on Monday to examine allegations of serious human rights abuses.

In New York, the U.N. Security Council on Friday expressed its “grave concern” about the deteriorating situation and called on all sides to show maximum restraint and engage in dialogue.

Amid the disorder, there are some signs that Islamic militants - some who have battled Yemen’s government and others who have been drawn into occasional alliances with it - are making gains. This week, nearly 60 al—Qaeda suspects broke out of a prison in Yemen.

The recent takeovers of Jaar and Zinjibar, a short distance to the east of Aden, were carried out with little resistance as security forces had already pulled out.

That raised accusations that President Saleh allowed the militants to sweep in to bolster his claims that without him in power, al—Qaeda would seize control of the country.

Mr. Saleh’s opponents have dismissed his warnings as overblown. Al—Qaeda in the Arabian Peninsula has an estimated 300 hard—core members, and is not seen as capable of seizing control on a wide scale.

The U.S. says the group is now the terror network’s most active branch. It has been linked to several nearly successful attacks on U.S. targets, including the plot to bomb a Detroit—bound airliner in December 2009 with a bomb sewn into the underwear of a would—be suicide attacker. The group also put sophisticated bombs into U.S.—addressed parcels that made it onto cargo flights last year but were caught before they exploded.

With the agreement of Saleh loyalists, the U.S. has carried out expanded strikes against al—Qaeda targets in Yemen with armed drones and warplanes in recent weeks.

A melting away of security forces appears to be under way in Aden.

“Where are the tens of thousands of security and military?” said Omar al—Marfidi, a 33—year—old civil engineer. “Their disappearance raises questions about whether they want to let the terror groups enter Aden and terrorize people.”

On Friday, residents said tank and artillery units were gone from the entrances of the city. Armoured vehicles in the suburbs and outside a major hotel disappeared. Security forces were still positioned around the presidential palace in Aden.

Residents in some districts have started to form popular committees to try to fill the security vacuum, according to Shaher Mohammed Said, an activist and city resident. “We have been hearing that militants have made it through to Aden, which makes us worried about our city,” he said.

The most visible security forces in Aden on Friday were those confronting tens of thousand of anti—government protesters who took the streets during a funeral procession for a young man beaten to death in police custody.

Forces backed by tanks fired to disperse the crowds, killing at least one person, a medical official said, speaking on condition of anonymity because he was not authorized to brief the media.

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