A massive hunt is under way for the bombers who wrought carnage on underground trains and blew up a double-decker bus in London, killing at least 37 people and injuring more than 700.

Prime Minister Tony Blair has promised to track down the perpetrators of the worst terror attack ever in Britain.

"There, of course, will now be the most intense police and security service action to make sure we bring those responsible to justice," the grim-faced British leader told the nation in a televised address.

Scotland Yard spokesman Alan Crookwood said the investigation was "a very high priority."

Three explosions tore apart packed underground trains and one peeled the top off a double decker bus Thursday.

Blood-spattered and crying, thousands staggered into the streets, the entire underground rail network was shut down and terror replaced the euphoria of the day before when London was named the host of the 2012 Olympic Games.

The synchronized blasts, detonated without warning, were over in 56 minutes:

-- 8:51 AM (07:51 GMT): a blast hits between Liverpool Street and Aldgate underground stations, killing seven people.

-- 8:56 AM  (07:56 GMT): an explosion detonates in the underground near the central King's Cross station. A further 21 die.

-- 9:17 AM (08:17 GMT): a device explodes at Edgware Road underground station, the western part of the center of the city, slicing through a carriage, a wall and, police say, into two other trains. Seven people are killed.

-- 9:47 AM (08:47 GMT): An explosion blows apart the number 30 double-decker bus from east London's Hackney to central Marble Arch. Two die.

British Foreign Secretary Jack Straw said Osama bin Laden's global terrorist network, Al-Qaeda, seemed to be behind the atrocities.

"These outrages bear the hallmarks of Al-Qaeda related terrorist cells," he said. "That is obviously the principle assumption on which the police and intelligence agencies are operating."

The country reacted with defiance.

"They should not and they must not succeed," said Blair, who interrupted a Group of Eight summit to fly London for a meeting of the government's emergency committee and to speak to the country.

"When they try to intimidate us we will not be intimidated. When they seek to change our country or our way of life by these methods we will not be changed. When they try to divide our people or weaken our resolve, we will not be divided and our resolve will hold firm."

Memories of the World War II blitz attacks on London overcame the press.

"Our spirit will never be broken," blared the front-page of The Sun, the country's best-selling tabloid. "If the terrorists want a fight, by God, we'll give it them."

The Times' editorial expressed "revulsion and resolve."

Witnesses related horrific scenes. "There was a big bang and then all the ash. I could not breathe. It was falling down everywhere and over everything," said Loyita Worley, who was in a carriage when a blast hit near Liverpool Street.

"Some people started to panic but most were okay. We tried to open the doors but the doors were fixed shut and the ash was settling everywhere," she said, and then came the walking wounded.

"There was blood dripping off them, they were all white."

The bus explosion, too, caused mayhem.

"It was terrible. The bus went to pieces. There were so many bodies on the floor," said Ayobami Bello, 46, a security guard at the nearby London School of Tropical Hygiene and Medicine.

A previously unknown group which calls itself the Organization of Al-Qaeda Jihad in Europe claimed it caused the blasts and threatened similar attacks against Italy, Denmark and other "Crusader" states with troops in Iraq and Afghanistan.

In a statement posted on the Internet, but which could not be authenticated, it said: "Heroic mujahedins carried out a sacred attack in London, and here is Britain burning in fear, terror and fright in the north, south, east and west."

The group said the attacks were "in response to the massacres carried out by Britain in Iraq and Afghanistan."

"We have repeatedly warned the government and people of Britain, and we have now fulfilled our promise and have carried out a sacred military attack in Britain," it said.

A stunned resignation reigned in London, with many forced to walk because of withdrawal of buses in the center and the shutdown of the entire underground railway, a network of 12 lines and 275 stations used by three million people daily.

The flag flew at half mast over Buckingham Palace.

"The dreadful events in London this morning have deeply shocked us all," Queen Elizabeth II said in a statement.

At the G8 summit in Scotland, leaders vowed support for Britain. "We condemn utterly these barbaric attacks. We send our profound condolences to the victims and their families.

US President George W. Bush promised to wage his "war on terror."

"They have such evil in their heart that they will take the lives of innocent folks. The war on terrorism is on," Bush told reporters at the summit venue, the luxury golf resort of Gleneagles.

In the United States, Homeland Security Secretary Michael Chertoff raised the threat level for mass transit and train systems to code orange or "high."

Security was stepped up in New York and Washington, still jittery after the September 11, 2001 attacks on the United States by the Al-Qaeda terror network, while the nationwide US rail system, Amtrak, also said it raised its security alert level.

Governments across Europe beefed up security in airports, rail stations and public transport systems.

In Singapore, the chief executive of London's victorious 2012 Games bid, Keith Mills, said Olympic celebrations would be put on hold. "It's terribly unfortunate in terms of timing and clearly all our celebrations of the result yesterday will have to be put on hold," he said.

World financial leaders appealed for calm on the markets. "We mustn't allow the situation to get out of hand by acting wrongly or panicking," German Finance Minister Hans Eichel said.

(Chinadaily.com via agencies July 8, 2005)