SAN'A, Yemen (AP) — A young Yemeni man who blew himself up in an attack on the British ambassador this week had been jailed for suspected ties to al-Qaida and vanished after his release from custody earlier this year, his father said Wednesday.

The 22-year-old bomber's father said he alerted police when his son disappeared after spending two years in prison. The young man, however, escaped detection and prepared to carry out a suicide operation, most likely at the direction of Yemen's al-Qaida offshoot, though there has been no claim of responsibility.

The British ambassador was unhurt in Monday's attack, in which the Yemeni man detonated his explosives belt near the diplomat's armored car in a poor neighborhood of the capital, San'a.

The suicide bombing was the first of its kind in the capital in a year. It cast doubt on the effectiveness of the Yemeni government's U.S.-backed campaign against al-Qaida militants, who have found a haven in parts of the rugged, mountainous nation where the central government's control is weak.

The bomber's father, Ali al-Salwi, said in an interview that authorities had agreed to release his son into parental custody earlier this year as long as he checked in with police daily and attended school. Instead, Othman al-Salwi disappeared without notifying his family of his whereabouts, his father said.

The ambassador's vehicle was passing through the impoverished Noqm district when the young bomber staged his attack. The explosion ripped apart the bomber, and his head was found on the roof of a house about 20 yards away, the Interior Ministry said.

Three bystanders were hurt in the attack.

Ali al-Salwi said police called him the same day and showed him a photograph of the bomber's severed head so he could identify him.

On Wednesday, Yemeni police raided homes of suspected militants in San'a and arrested a number of people, a security official said on condition of anonymity because he was not authorized to speak to the media. He would not provide further details.

Yemen says it is waging an aggressive campaign to uproot al-Qaida, and Washington has earmarked some $150 million in military assistance to the government to help combat the threat with training, equipment and intelligence help.

Al-Qaida in the Arabian Peninsula, an offshoot of Osama bin Laden's terror network, was formed more than a year ago when Yemen and Saudi militant groups merged. Militants are believed to have built up strongholds in remote parts of the country, allying with powerful tribes that resent the government of President Ali Abdullah Saleh.

The group's fighters attacked the U.S. Embassy in San'a twice in 2008, and earlier this year a number of Western embassies, including the U.S. and British, shut down for days in response to threats of attack.

The Nigerian suspect in the failed Christmas Day plot to bomb a Detroit-bound airliner has said he received training from al-Qaida militants in Yemen, according to U.S. investigators. In February, the offshoot's military commander, Qassim al-Raimi, warned of further attacks against Americans.

Besides the al-Qaida threat, Saleh's government is facing a secessionist movement in the south and has struggled with a five-year rebellion with minority Shiites in the north. Saleh also has maintained alliances with Islamic extremists in a bid to assure their support in the country's multiple conflicts.