Making a major breakthrough in last week's bombings in London, the police on Tuesday arrested one person following raids on residences in Leeds in northern England and seized a car in Luton.
The police also believe that at least one of the suspected bombers died in Thursday's blasts that killed 52 people and injured 700 others.
"One man has been arrested in West Yorkshire and will be brought to London to be questioned," Deputy Assistant Commissioner Peter Clarke told a press conference in London.
However, Sky News television, quoting police sources reported that all four suspected bombers died during the serial bombings in London. Three bombers died in separate Tube attacks, while another was killed in the bus blast at Tavistock Square.
The television station also said that all four suspected bombers were British citizens.
Clarke said at least three of the suspected bombers came from West Yorkshire, where police carried out raids earlier in the day. The home addresses of the three suspects were among the residences raided by the police.
Clarke, who heads the Metropolitan Police anti-terrorist squad, said one bomber had died in the explosion between Aldgate and Liverpool Street Underground stations.
Close Circuit Television footage showed that all four suspects had arrived at King's Cross station by 8:30 am on Thursday, about 20 minutes before the blasts on the three Tube trains, he said.
There was evidence of personal possessions and forensics suggesting all four may have died in the explosions, Clarke said.
He said that police found a vehicle at the railway station car park in Luton, thought to be linked to Thursday's bombings.
One of the men from West Yorkshire had been reported missing by his family and his property was found at the bus blast scene, he said.
"The investigations are going at great speed," Clarke said.
Meanwhile, carrying out investigations into racist revenge attacks after the bombings, the police also arrested five people on suspicion of attempting to bomb a gurdwara. Another person was charged in connection with hoax calls in a place of worship.
Earlier the police carried out controlled explosions in Leeds and Luton and searched six houses. They blasted their way into an unoccupied house in the Burley area of Leeds in search for clues of perpetrators of the attacks.