A Briton identified by Pakistan as a key suspect in the London airliner terror plot has links with outlawed Pakistani militant group Jaish-e-Mohammed and is related by marriage to its leader, an intelligence official and a relative said.

Rashid Rauf, arrested here last week in connection with the alleged conspiracy to blow up U.S.-bound jetliners, left the group about two years ago and forged ties with Al Qaeda militants, the intelligence official said Thursday.

Separately, Pakistani authorities said they are searching for three more suspects they believe may be linked to the foiled plot — a British Muslim of Afghan origin, an Eritrean national and a Pakistani.

Suspects already detained in Britain and Pakistan, including Rauf, have told interrogators of the three new suspects believed to be at large in Pakistan, intelligence officials said on condition of anonymity due to the sensitive nature of the inquiry. No further details were provided.

In Bhawalpur, an eastern Pakistani stronghold of Jaish-e-Mohammed, a man claiming to be Rauf's brother-in-law said police detained the terror suspect as he tried to leave the town on a bus to the nearby city of Multan on Aug. 9 — two days before suspects were rounded up in Britain.

The town lies about 300 miles southwest of Islamabad.

Hafiz Mohammed Sohaib, who teaches at an Islamic school here, told The Associated Press on Wednesday that his sister married a man by the name of Khalid Rauf three years ago. Police told Sohaib's family that Khalid was an alias for Rashid Rauf.

Several days after his arrest, police commandos and plainclothes officers raided Rauf's home and confiscated a computer and identity documents, Sohaib said.

Sohaib did not know if Rauf held British citizenship and knew him only as a seller of refrigerators.

Sohaib said his other sister is married to the brother of Maulana Masood Azhar, the wanted head of the Jaish-e-Mohammed, a militant group that fights Indian security forces in Kashmir and has been blamed by India for a deadly attack on India's parliament in December 2001 that almost sparked war with Pakistan. The group has also had links with the Taliban.

The intelligence official, who spoke on condition of anonymity because of the secretive nature of his job, confirmed that Rauf was linked by marriage to Azhar.

But a Jaish-e-Mohammed spokesman denied on Thursday that Rauf had ever been a member of the group. "He had never been a member (of Jaish-e-Mohammed). We have not even seen his face," said Mufti Abdur Rauf.

Rauf, a British national of Pakistani descent aged in his 30s, had also been in contact — through intermediaries — with the purported No. 3-ranked Al Qaeda leader at large in neighboring Afghanistan, and had met Al Qaeda figures inside Pakistan in the lead-up to his arrest, intelligence officials said.

Rauf is one of up to 17 suspects, including a second, unidentified Briton, arrested in Pakistan in connection with the London terror plot. His brother, Tayib Rauf, is among the plot suspects detained in Britain.

Pakistani intelligence officials say the would-be London plane bombers wanted to carry out a large-scale Al Qaeda-style attack to mark the fifth anniversary of the Sept. 11 strikes, but were too "inexperienced" to carry out the plot.

Rashid Rauf moved to Pakistan shortly after his maternal uncle was stabbed to death in April 2002. He was reportedly a suspect in that murder and police raided his Birmingham home as part of the homicide probe.

Another Pakistani official said a court had approved an extension to Rauf's detention to enable further interrogations. It was unclear how long the detention period had been extended for. British and Pakistan officials have suggested Rauf could be soon extradited back to Britain.