The United States vowed on Wednesday to strike back with a ``hammer of vengeance'' for the attacks on the World Trade Center and the Pentagon, while clues emerged the hijackers most likely came from the Middle East.
FBI agents conducted searches in Massachusetts and Florida and reports said they had identified at least some of the hijackers who rammed three commercial jets on Tuesday into the Pentagon and the twin towers of what was once the world's tallest building, the World Trade Center, reducing it to rubble and a mass grave for possibly thousands of people.
While rescue workers tried desperately to pull survivors from the wreckage, President Bush committed the country to a ''monumental struggle of good versus evil.''
He worked through the day to build a global coalition against ``terrorism'' while officials said he was a possible target of attack. They said they had credible evidence the hijackers wanted to attack the White House and Air Force One.
Bush, facing the defining moment of his eight-month presidency, called the attacks ``acts of war.''
As a sign of support for the president, NATO invoked its mutual defense clause for the first time in its 52-year history, opening the way for a possible collective military response to the shattering attacks.
FOCUS ON MIDEAST LINKS
Bush also visited the Pentagon, which was reopened for limited business on Wednesday. Nearby, rescue teams searched through rubble for up to 200 or more missing defense workers. To greet him workers hung a giant American flag from the roof.
Dozens of firemen finally put out a stubborn roof fire at the Pentagon more than 24 hours after a hijacked fuel-laden airliner slammed into a corner of the five-sided building.
Investigators hunting for those behind the worst attack on the country since the Dec. 7, 1941, attack on Pearl Harbor cast a wide net.
Senior US officials said initial evidence pointed to the organization of Osama bin Laden, the Saudi-born dissident now living in Afghanistan who is blamed for bombing two US Embassies in East Africa and other anti-American attacks.
Attorney General John Ashcroft said the hijackers worked in teams of between three and six people and used knives and box cutters, plus the threat of bombs, to commandeer the planes.
Sen. Kay Bailey Hutchison, a Texas Republican, told reporters after an intelligence briefing, authorities in Boston had recovered a flight manual in Arabic from a bag that was believed to have belonged to one of the hijackers.
Boston newspapers said earlier officials had identified five Arab men as suspects and seized a rental car at the city's airport containing Arabic-language materials.
Investigators found a copy of the Koran, a videotape on how to fly commercial jets and a fuel consumption calculator in a pair of bags meant for American Airlines Flight 11, which crashed into the World Trade Center, the Boston Globe said.
Hutchinson said it was thought at least one of the men had entered the United States from Canada. The Boston Herald said two of the five men were brothers whose passports were traced to the United Arab Emirates, and one was a trained pilot.
US agents also searched homes and businesses in south Florida, and issued alerts for two cars in connection with the attacks. Media attention focused on one of the men listed on the flight manifest of one of the hijacked planes.
Transport officials cleared airlines for limited flights after an unprecedented national grounding of all flights on Tuesday. But they also introduced tighter security rules that will end curb-side check-ins and prevent anyone from carrying a knife onto a plane.
Financial markets remained closed at least until Friday. Americans attended prayer vigils, hung flags and braced for a death toll expected to climb well into the thousands.
PASSENGERS SAID TO FIGHT BACK
In Boston, heavily armed police and FBI agents swarmed a downtown hotel in what appeared to be a search, while police in Providence, Rhode Island, removed three passengers from am Amtrak train. But FBI Director Robert Mueller said no arrests had been made.
Two of the four hijacked planes were from Boston's Logan airport; they were later flown directly into New York's World Trade Center, toppling the 110-story structures.
A third jetliner seriously damaged the Pentagon, while a fourth crashed in Pennsylvania.
The Washington Post's Internet site gave a harrowing account into the final moments of that flight when passengers made a desperate bid to overpower the hijackers.
Minutes before the giant airliner smashed into a field, passenger Jeremy Glick used a cell phone to call his wife at home in New Jersey and told her that he and several other people on board had resolved to resist the hijackers, according to Glick's brother-in-law, Douglas Hurwitt.
``He knew that stopping them was going to end all of their lives,'' Hurwitt said. Glick explained to his wife, Lyzbeth, the plane had been taken over by three Middle Eastern men wearing red headbands.
Anticipating death, Glick, 31, wished his wife a good life and told her to take care of their 3-month old baby girl.
Ashcroft said it appeared a number of suspected hijackers had been trained as pilots in the United States.
In New York, where smoke continued to billow over the skyline, Mayor Rudolph Giuliani said the death toll would rise into the thousands as more and more bodies were found.
``The best estimate we can make...is there will be a few thousand people left in each building,'' he said. Around 40,000 people worked in the monolithic high-rises.
A FEW RESCUED
Giuliani said three people had been rescued from the debris and he hoped more survivors would be found. A list of tenants from Trade Center read like a ``Who's Who'' of international finance, underlining Manhattan's key role in global markets.
In northern Virginia, officials said the death toll at the US military headquarters was likely around 200 -- less than initially feared.
At the nation's airports, officials said tight new security measures would permanently alter the way travelers take to the skies, ending curb-side check-in, restricting access to secure areas, and stepping up random identification checks.
Arizona Sen. John McCain described the national mood as one of ``controlled fury.'' Congressional leaders agreed to a $20 billion recovery package, in response to a request from the White House.
Secretary of State Colin Powell said would ``tee up'' a possible collective response once the United States identified the perpetrators and their sponsors.
Powell said a US response would surpass a single reprisal raid, while defense officials stressed the culprits would be punished. ``We have a very large hammer that can be brought to bear in a number of ways at any time,'' one of the officials told Reuters. ``That's not a threat, it's a fact.''
Powell called for a global coalition to fight ``terrorism'', including NATO, Russia, China and also Muslim countries.
``We have to make sure that we go after terrorism and get it by its branch and root,'' he told a news conference.
A Pakistani newspaper said bin Laden had denied blame. ``The terrorist act is the action of some American group. I have nothing to do with it,'' it quoted him as saying.