The BBC's Gareth Jones reports on the devastation in Omagh

At least 27 people, including an 18-month-old infant, have been killed in the worst paramilitary bombing since the start of the Northern Ireland conflict 30 years ago.

Political leaders have been joined by the Queen in expressing their sympathy for the bereaved and those injured in the explosion in the market town of Omagh.

British Prime Minister Tony Blair: "Terrorists will not win"

The blast left more than 100 people injured or maimed. Both Protestants and Catholics were hurt and killed.

Martin McGuinness, the chief negotiator for Sinn Fein, said: "This appalling act was carried out by those opposed to the peace process.

"It is designed to wreck the process and everyone should work to ensure the peace process continues."

A BBC correspondent said the statement was the strongest condemnation of an act of paramilitary violence by the party which represented the IRA in the Stormont talks.

Suspicion falls on "Real IRA"

No group has claimed responsibility for the bomb, which was planted in a maroon Vauxhall Astra.

RUC Chief Constable Ronnie Flanagan: "I just can't find the words to describe the horror inflicted on the people of Omagh"

RUC Chief Constable Ronnie Flanagan said: "Undoubtedly we will be focusing our attention on those who call themselves the 'Real IRA'. It is possible and probable that they carried out this attack.

"These are people who have murdered here today because they want to murder."

The Northern Ireland Secretary, Mo Mowlam, is flying back from Greece, where she had been on holiday, and plans to visit Omagh.

Scenes of utter carnage

People who survived the car bomb blast in a busy shopping area of Omagh, County Tyrone, have been describing scenes of utter carnage with the dead and dying strewn across the street and other victims screaming for help.

BBC Ireland correspondent Tom Coulter: "Worst single act of terrorism in Northern Ireland in 30 years"

Police were clearing an area near the local courthouse, 40 minutes after receiving a telephone warning, when the bomb detonated.

But the warning was unclear and the wrong area was evacuated.

The bomb was planted in a maroon Vauxhall Astra

Instead, people were being directed towards the device when it went off shortly after 1500 (BST).

Women and children - one just 18 months old - are among the dead, many of whom, only moments before the blast, had been standing behind white tape which police had erected when clearing the streets.

SDLP councillor Joe Byrne: "Wreckers must not succeed"

Publican Nigel O'Kane said: "It was totally indiscriminate. Police were pushing everyone towards the bottom end of the town not knowing the bomb was there.

"It went off outside one of the busiest shops in the town flattening it and the one beside it."

There were reports that the town was holding its annual carnival when the blast happened.

Casualty figures

The ambulance service said at 1630 (BST) that "up to a dozen" people had been killed.

At 1820 (BST), the number of confirmed dead had risen to 21.

A trail of blood leading up the steps of Tyrone County Hospital illustrated the destruction caused by the bomb.

The area around the courthouse was being cleared when the bomb went off

As dozens of worried relatives gathered outside, porters cleaned blood from the trollies used to ferry the injured and dying.

Catholic priest, Father John Ryder was almost lost for words. He said the scene inside the hospital was "chaotic" but staff were doing marvellous work.

"So many families uncertain, just coming along and not knowing what to do.They are distraught because some of them don't even know yet whether they've anybody here or not."

Hospital spokeswoman, Glynis Hendry, said a number of critically and seriously injured people were being treated.

"A lot of staff have come in from off-duty and a lot of staff from the community have come to help us," she added.

A BBC correspondent says "dozens, upon dozens, upon dozens" of people have been injured. Some have lost limbs, many were cut by flying debris.

Some victims were being transferred to the Royal Victoria and South Tyrone Hospitals.

Fifty-four casualties, many of them walking wounded, have been admitted to Erne Hospital, Enniskillen, and more were arriving.

A number of people responded to their appeal for blood and were liaising with the laboratory.

'Savagery and evil'

The Prime Minister, Tony Blair, is being briefed minute by minute by officials while on holiday in France.

He condemned the attack as an "appalling act of savagery and evil" by people determined to wreck the peace process.

The Queen: "Expression of sympathy"

In a statement, he pledged that the bombers would be pursued "to the utmost" in order to bring them to justice. "These people will never be allowed to win."

The Queen also issued a statement saying: "Please pass my heartfelt sympathy to the bereaved, injured and those others who have suffered in their distress".

Ulster Unionist security spokesman Ken Maginnis said he believed there had been at least 100 casualties.

"This is a dreadful crime against humanity," he told BBC News 24.

No-one has yet claimed responsibility but suspicions will fall on dissident republican groups, such as the "Real IRA".

The RUC has set up a casualty bureau to deal with inquiries from the public. The number is 01232 673371.