The BBC's Peter Hunt: An explosion like a clap of thunder

It was the third nail bomb attack in the capital inside three weeks following explosions in Brixton and Brick Lane.

Surgeons were operating on a further four people early on Saturday morning and several more were still said to be seriously ill.

The bomb, packed with nails, exploded without warning at 6.35pm on Friday in the Admiral Duncan pub in Old Compton Street in Soho - a regular meeting place for the capital's gay community.

The locations of the nail bombs

A right-wing terror group, the White Wolves, later claimed it planted the device.

Police have arrested four men in connection with bombings.

One was arrested in Hampshire in the early hours of Saturday and will be questioned by detectives later.

A man in his early 20s was arrested on Friday evening in east London. Earlier on Friday a man was arrested in Surrey.

A man, arrested on Thursday, was bailed by police to return at the end of the month.

One witness described the scene in Soho as "absolute carnage". Several people were blown out of the pub into the street that just moments earlier had been full of Bank Holiday revellers enjoying the sunny evening at bars and restaurants.

Those caught in the blast fled into the surrounding tight streets before police cleared the area.

Some of the injured lost limbs and suffered severe burns.

Doctors and a medical team from the Royal London Hospital, Whitechapel, were flown to the scene, landing by helicopter in Trafalgar Square.

A block away from the blast scene, in Soho Square, paramedics set up an emergency field hospital while ambulances ferried victims to four London Hospitals.

At least 20 were kept in hospital overnight. Some of the victims - mostly men in their 20s and 30s - had limbs blown off, and others suffered serious flash burns.

'Similar devices'

Forensic scientists and anti-terrorist squad officers spent the night combing the scene for clues.

An injured man flees the scene

They are now trying to establish whether there were any CCTV cameras in the area that may have captured the bomber on film.

A far-right splinter group, the White Wolves, later telephoned a BBC newsroom, claiming responsibity for the Soho explosion.

Police are linking all three attacks, saying the devices were similar.

Last Saturday's blast in Brick Lane, east London, which injured six people, was at the heart of the Bangladeshi community in London.

And 39 people were hurt the previous weekend in Brixton, south London, which has a large black community.

Sir Paul Condon, Commissioner of the Metropolitan Police, told a news conference: "These are cowardly hate attacks.

"We will defeat the people responsible for these bombs. We will catch them."

Jack Straw: We are dealing with people who have no humanity whatsoever

Home Secretary Jack Straw said: "The British people will not be intimidated by this kind of outrage."

Sophie Holland, 17, who works in Old Compton Street, said she had visited the Soho pub's barmaid, Veronica, at St Thomas's Hospital.

"She saw the bag and she was worried about it, but was pouring a beer at the bar at the time," said Ms Holland.

"As she went to go towards it the bomb went off. She said there was a big bang and it was blinding for her, and her hearing was impaired."

Eyewitness Jim Davies describes the scene

Another eyewitness, Jim Davies, said the scene was so bad it looked as though someone had "thrown a bucket of blood around".

"There was a massive bang," he said. "The pub was very busy - there must have been 40 people in there. It looked as though people were blown out into the street.

Ken Murphy, a motorcycle paramedic with the London Ambulance Service, was first on the scene.

Two injured men stand outside the pub

He said there were numerous casualties, including two with "traumatic amputation of limbs".

Scotland Yard's Deputy Assistant Commisioner Alan Fry said he was anxious to hear from anyone seen acting suspiciously inside or in the vicinity of the Admiral Duncan pub.

He added: "I would appeal to the public to remain vigilant. If you see any unattended package or bag, dial 999 and move away as soon as possible."

Friends or relatives worried about the injured can telephone Scotland Yard's casualty bureau on 0171 834 7777.

Anyone with information should contact the police, in confidence, on the anti-terrorist branch hotline on 0800 789321