Authorities have arrested an Egyptian chemist for questioning about a possible role in the suicide attacks last week on London's public transportation system, the Interior Ministry said Friday.

The ministry identified the man as Magdi Mahmoud Mustafa Nashar, 33, a biochemical researcher at Leeds University in Britain. It said he was on a six-week vacation in Cairo, where his family lives, and had planned to return to London afterward. He denied to interrogators that he played any role in planning the July 7 attacks, which killed at least 54 people, including four suicide bombers, and injured more than 700.

"He pointed out that all of his belongings were still in his apartment" in Britain, the statement said.

In London, police said Friday the attack bore the hallmarks of the al Qaeda terrorist network and vowed to track down others who might have been involved, such as anyone who provided the explosives, training or financing for the bombings.

In Pakistan, Reuters news agency reported, security forces investigating connections to the London bombings arrested four suspects Friday in the city of Faisalabad, where one of the suicide bombers met with a member of an al Qaeda-linked militant group two years ago.

The arrest of Nashar, a man who went from a hard-scrabble neighborhood on Cairo's outskirts to a successful academic career in the United States and Britain, marked a broadening of the investigation into the attacks, the worst instance of terrorism on British soil.

Given Nashar's travels -- his studies took him from Cairo to North Carolina to Leeds -- his whereabouts were certain to interest U.S. and British investigators, as well as those in Egypt, who remain deeply wary of Islamic militancy. Beyond the ministry statement, Egyptian officials said little about the arrest or whether Nashar was considered a witness or suspect.

British media have reported that Nashar rented a house that was raided by police on Tuesday in Leeds, a diverse industrial town in northern England where three of the four bombers lived. Media reports said a search of the home had turned up explosives similar to those found in the shoes of Richard Reid, a British citizen known as "the shoe bomber," after an unsuccessful attempt to blow up a U.S.-bound airliner in 2001.

Word of Nashar's detention prompted surprise among Egyptian neighbors who grew up with him along a leafy but poor and crowded street near the wealthy Cairo neighborhood of Maadi. He was remembered as a somewhat quiet, polite youth, who lived with his parents and a younger brother and sister in a modest, second-floor apartment in a narrow street prone to ruptures of sewage pipes.

"He wasn't involved in anything political," said Mustafa Mahmoud, a 41-year-old day laborer. "Look at the area. We all live next to each other, we all know everything about each other, and I know there wasn't anything political about him."

Nashar reportedly was arrested in Cairo within the past week. Colleagues said he arrived in Cairo about two weeks ago -- roughly a week before the bombings, the Associated Press reported.

Nashar studied chemical engineering as a graduate student at North Carolina State University in Raleigh for a semester beginning in January 2000, the university has confirmed.

He then went to Britain to continue his studies, arriving at Leeds University in October 2000 to do biochemical research under the sponsorship of Egypt's National Research Center. He earned a doctorate in May and taught chemistry at the university.

According to the Times of London and the British Broadcasting Corp., a search of an apartment rented by Nashar in Leeds indicated that triacetone triperoxide, or TATP, had been used to build a powerful explosive there. TATP was one of the compounds used by Reid, "the shoe bomber," in his attempt to blow up an American Airlines flight from Paris to Miami in December 2001.

British police would not comment on the reports and so far have refused to specify the type of explosives used in the July 7 bombings.

Reid, the London-born son of an English mother and Jamaican father and a convert to a radical brand of Islam, tried to light a fuse connected to explosives in his shoes but was overpowered by other passengers and arrested on arrival in the United States. He was subsequently sentenced to life in prison.

Three of the suspected London suicide bombers were British citizens of Pakistani origin, and the fourth was an immigrant from Jamaica.

Authorities in Pakistan are investigating possible connections between at least one of the bombers, Shahzad Tanweer, 22, and two militant groups liked to al Qaeda.

British police have confirmed that Tanweer was among the attackers who traveled to London from West Yorkshire on the morning of July 7 and that he was responsible for a suicide bombing on a subway train at Aldgate.

The commissioner of the Metropolitan Police, Ian Blair, said in television interviews Friday that if necessary, Britain would seek the extradition of Nashar, since the aim of the investigation is to put those responsible for the bombings on trial.

He said in an interview shown on CNN that the July 7 attack "has the hallmarks of al Qaeda: the simultaneous explosions, the fact that the dead appear to be sort of foot soldiers."

Blair added, "What we've got to find is the people who trained them, the people who made the bombs, the people who financed it."

Branigin reported from Washington.