Police arrested seven people Sunday during a raid on an apartment in southern England, bringing to 21 the number in custody in the relentless hunt for accomplices in the failed July 21 transit bombings.

Investigators determined to prevent further attacks also were probing possible ties between two of the bombing suspects and Saudi Arabia (search), British newspapers reported. Police were searching for anyone who may have recruited and directed the attackers and built the explosives.

Police arrested the six men and one woman during a search of two buildings in Brighton (search), on the southern coast, said a Metropolitan Police spokeswoman, speaking on condition of anonymity because her department does not allow her to give her name. So far, 18 people have been arrested in Britain and three in Italy.

She said police believed there were more people at large who were involved in the July 21 attacks, in which four bombs partly exploded, and the deadly July 7 bombings.

Both attacks targeted three subway trains and a double-decker bus. All the July 7 attackers were believed dead; police have in custody four suspects they believed planted the explosives July 21.

"It's extremely likely there will be other people [who were] involved in harboring [suspects], financing and making the devices," the spokeswoman said.

Key suspects were being interrogated in London in relation to the failed July 21 attempts, police said. In Italy, authorities were pursuing contacts linked to Osman Hussain (search), 27, who was arrested in Rome on Friday and is suspected of trying to bomb the Shepherd's Bush subway station in west London.

Police have discovered that Hussain called Saudi Arabia hours before his arrest, the Sunday Telegraph newspaper reported, and the Sunday Times said another bombing suspect — Ethiopian-born Briton Muktar Said Ibrahim, 27 — took a monthlong trip to Saudi Arabia in 2003, telling friends he was receiving training there.

Britain was facing questions about how Hussain, also known as Hamdi Issac, slipped out of the country during a massive police manhunt. Italy's Interior Minister Giuseppe Pisanu says Hussain left London's Waterloo station by train on July 26.

The Home Office said immigration officials generally do not check the passports of people leaving the country. However, police had asked that checks be made at many departure points after the attacks, including Waterloo, a Home Office spokesman said on condition of anonymity, according to government policy.

Geoff Hoon, leader of the House of Commons, said he realized there was concern about whether the checks were stringent enough.

"I am aware that the Home Office will be looking at that," he told British Broadcasting Corp. television. "I understand the criticism. It's important that we are able to identify those coming into the country as well as those leaving."

Police had released closed-circuit television images of the four bombing suspects shortly after the attacks, but the picture of Hussain, whose name was not made public until his arrest, was grainy and his face difficult to see. Police put out a clearer image of him a day after his escape.

Italian news reports said Hussain's real name was Hamdi Issac and that he was from Ethiopia, not Somalia. He falsely listed his country of origin as Somalia when he applied for asylum and citizenship in Britain, the reports said.

Hussain was arrested Friday in Rome at the apartment of his brother Remzi Issac, who also was detained.

On Sunday, Italian police detained a second brother of Hussain, Fati Issac, for questioning, the Italian news agency ANSA said. Fati Issac was accused of destroying or hiding documents sought by investigators, ANSA said

Britain has requested Hussain's extradition, which his court-appointed lawyer, Antonietta Sonnessa, said he is likely to fight.

She said Hussain acknowledges his involvement in the attack but claims the planted bombs were intended not to kill anyone but only to draw attention. Italian news reports had said the bombers were angry about the Iraq war.

"He has justified his actions as a form of protest against the fact that civilians are suffering in wars at the present time," she told Britain's ITV News.

"He is not at all a violent person, and made sure he would not cause any damage, injuries or deaths," she said. "His action was to explain to the British public how difficult life is in countries where war is a daily event."

Hussain also told investigators his cell was not linked to either Al Qaeda or those who carried out the July 7 attack, Italian news reports said.

His lawyer said the plot was loosely organized, put together at the last minute.

"There wasn't a very clearly defined plan, the whole thing was set the day before, in a meeting with this group of friends," Sonnessa said.

In addition to the arrests Sunday, police in Manchester, in northern England, detained a man at a train station under anti-terrorism legislation but said they did not believe he was linked to the London bombings. Inspector Mohammed Sultan gave no further details about the arrest at Stockport station.

In London, the Home Office said a top official would meet with Muslim leaders around Britain to discuss fighting extremism. Three of the four July 7 bombers were Pakistani Britons, and their willingness to kill has raised troubling questions about militant Islam's appeal to some young Britons. Most of the July 21 attackers were immigrants from east Africa.

Spain's intelligence chief dismissed the possibility that the London bombings were connected to the train bombings in Madrid that killed 191 people last year.

Alberto Saiz, director of the National Intelligence Center, told the daily El Pais that similarities between the attacks were limited to "their outward appearance" and the targeting of transport networks.

"At that point, the differences start," Saiz was quoted as saying, noting particularly that two sets of attacks had been carried out in London.

"In contrast to Madrid, this gives us the feeling that they are coordinated with other groups or have direction from above — and that there is a plan," he added. "This is not an isolated group that decides to act on its own account."