All four suspects wanted in connection with the failed 21 July attacks in London are tonight said to be in custody.
Two were held after separate raids in London. The fourth was held in Rome today, where Italy's interior minister Giuseppe Pisanu said the man was described as a Somali called Osman Hussain, a naturalised British citizen.
One of the two held in London was believed to be Muktar Said-Ibrahim, 27, who allegedly tried to blow himself up on a number 26 bus in Hackney, east London.
The other - as yet unnamed - is believed to have been responsible for an attempted bombing near Oval Tube station. A third man was also arrested as armed police launched two raids in west London this morning - and some reports linked him with the so-called fifth bomber.
Police are still questioning Yasin Hassan Omar. He was arrested on Wednesday in Birmingham and was sought in connection with the attempted attack on the Warren Street Tube train.
In London one of the armed raids ended in a siege at a flat on an estate near Wormwood Scrubs Prison in west London.
Among the names shouted by police at the flat in Block K of Dalgarno Gardens were "Mohammed" and "Mr Ahmed".
Witness Philomena Daly said: "I heard them say 'Mr Ahmed, come to the door'."
She saw two policemen dressed in blue overalls taking a man in a white forensic suit out of the estate. Until today, police had arrested only one of the bomb suspects. Yasin Hassan Omar, a 24-year-old Somalian alleged to have tried to set off a bomb on a train near Warren Street, was held during an operation in Birmingham on Wednesday morning.
Detectives believe there was also a fifth bomber because a fifth device was found in a rucksack dumped on open ground at Little Wormwood Scrubs, a few hundred yards from today's siege.
It is believed the fifth bomber may have tried to detonate his device on a bus or train but no one noticed and he dumped it.
Today's siege took place at a block of flats owned by the Peabody Trust and involved elite plainclothes firearms officers and snipers from Scotland Yard's SO19 unit.
Nicolas Holliman, who lives on the 350-property estate, said he had seen four officers with guns and rifles and a specialist firearms officer in a gas mask.
They were focusing on a top-floor flat in one of the blocks on the estate and kept asking for "Mohammed" to come out.
"He was being asked to come out with his hands up, naked or in underclothes," he said.
"They were giving directions for him to come out, telling him he would be safe if he puts his hands up."
Mr Holliman said he could tell there was more than one man in the flat by the way police were shouting and there were vocal protests coming from the flat.
Another witness said one of the suspects was heard shouting "I've got rights".
After some time, Mr Holliman said he heard several shots which he believed were gas being fired at the flat and then there was silence.
Witness Lisa Davis phoned Sky News and while she was talking on live television, police could be heard in the background shouting at " Mohammed" and telling him: "You must do what we say."
Ms Davis said: "We have got two men standing outside the flats right now. They have got their guns pointing upwards at the flat.
"'Take your clothes off' is what they are telling him, 'exit the building'.
"'Walk into the corridor and stop' is what they are telling him right now.
"They are asking him does he understand. They keep asking him 'Is there a reason that you shouldn't leave the flat?'.
"They have been saying this to him for about half an hour."
She said the officers had been trying to reassure the man that he would be safe.
In the other raid less than a mile away, dozens of officers, some wearing gas masks, swooped on the Tavistock Crescent area of Notting Hill, clearing a wide area and cordoning off streets. Snipers were stationed behind parked cars.
During the day there were reports of explosions and gunshots from residents near the raids.
But the explosion is thought to have been police blowing the door off a flat and the "shots" were stun grenades or CS gas.Reuse content