The British ambassador in Yemen narrowly escaped a homicide attack Monday, when a young man in a school uniform detonated his explosives belt near his armored car at a poor neighborhood of San'a, officials said.

The attack -- the first such bombing in the capital in a year -- raised questions over the Yemeni government's U.S.-backed campaign against Al Qaeda militants, who have found a haven in parts of the mountainous, impoverished nation where the central government's control is weak.

Washington has dramatically stepped up counterterrorism aid to San'a over the past year, warning that Al Qaeda's offshoot in Yemen has become a global threat, particularly after it claimed responsibility for the failed Christmas Day attempt to bomb an American jet liner heading for Detroit.

A British Embassy spokeswoman said the ambassador, Timothy Torlot, was unhurt in the attack Monday morning, which wounded three bystanders, including a woman.

The ambassador's vehicle was passing through the impoverished San'a district of Noqm when the explosion went off nearby, the Interior Ministry said in a statement. The explosion ripped apart the bomber, and his head was found on the roof of a house about 20 meters (yards) away, it said.

The ministry identified the bomber as a 22-year old high school student who hails from the southern town of Taiz.

Witnesses said the attacker was a young man who wore a school uniform, apparently as a disguise. Yemeni officials said the attacker was believed to have been wearing an explosives belt, adding that the Noqm district is known to be popular with militants.

The officials spoke on condition of anonymity because they were not authorized to speak to the media.

There was no claim of responsibility for the attack, but it bore the hallmarks of Al Qaeda.

In March 2009, a similar attack was carried out against a convoy carrying South Korean officials in Yemen, though the blast by a man wearing an explosives belt caused no injuries. The officials had been sent to Yemen to investigate a bombing earlier in the week that killed four Korean tourists at a historical site outside the capital.

The Foreign Office in London said the British Embassy in San'a has been closed to the public and warned all British nationals in Yemen to "keep a low profile and remain vigilant."

"We can confirm that there was an incident in San'a this morning. There was a small explosion beside the British Ambassador's car. He was unhurt. No other embassy staff or British nationals were injured," the Foreign Office said in a statement.

"We are working urgently with the Yemen authorities to investigate what happened," it added.

Security was visibly tightened around the U.S. and British embassies following the attack. The area of the explosion was sealed off as Yemeni and British officials inspected the scene of the attack.

Yemen has been embroiled in a war against the Al Qaeda militants, who have threatened to target foreign interests and diplomatic missions. Earlier this year, a number of Western embassies, including the U.S. and British embassies, shut down for days in response to threats of attack by an Al Qaeda offshoot in Yemen.

Al Qaeda gunmen backed by two car bombs attacked the U.S. Embassy in September 2008, killing 19 people, including an American woman and six militants. In March that year, mortars were lobbed toward the embassy but missed, hitting a girls' school nearby and killing a security guard.

Yemeni troops have been deployed in remote areas where Al Qaeda is known to have set up strongholds, and they carried out a series of U.S.-backed raids against militant hideouts at the beginning of the year.

Al Qaeda in the Arabian Peninsula, an offshoot of Usama bin Laden's terror network, was formed more than a year ago when Yemen and Saudi militant groups merged. The suspect in the failed Christmas Day plane bombing plot has said he received training from militants in Yemen, according to U.S. investigators.

The Associated Press contributed to this report.