Military aircraft patrolled the skies over major US cities on Thursday as officials pledged to wage "the first war of the 21st Century" against shadowy militants believed responsible for the worst attack ever staged on American soil.
A nervous nation reopened its airports while countless bomb threats emptied buildings across the country -- including the US Capitol, where lawmakers were interrupted by evacuation orders as they met to discuss emergency funds to help the nation recover from Tuesday's terror attack.
President George W. Bush, wiping tears from his eyes, vowed to "whip terrorism" and officials focused on exiled Saudi dissident Osama bin Laden, an implacable US foe with a global network of supporters.
Officials decided to move Vice President Dick Cheney from the White House to the Camp David presidential retreat in Maryland as a "precautionary measure," separating the nation's two top leaders.
In New York, rescue workers searching the ruins of the World Trade Center, where officials said 4,763 people were still unaccounted for after two hijacked planes destroyed the twin towers that anchored the nation's financial district.
Tearful New Yorkers clutching pictures of missing friends and relatives roamed the streets, while across the country anxious Arab-Americans worried about reprisals.
Worried international economic officials sought to counter growing fears the terror attack could trigger a global recession, while the resumption of stock trading was postponed until Monday.
IS BIN LADEN TO BLAME?
Secretary of State Colin Powell became the first senior US official to publicly identify bin Laden as a suspect for Tuesday's airplane attacks, which crumbled the 110-story World Trade Center towers and left 200 people either killed or unaccounted for at the Pentagon.
But aides to Bin Laden, accused of engineering attacks on US embassies in Africa in 1998 from his Afghanistan headquarters, told journalists in Pakistan that the shadowy leader denied involvement in the attacks, which he described as "punishment from almighty Allah."
With officials mulling retaliation options ranging from heavy bombing to elite troop strikes, one senior official told reporters that more than one extremist organization may have been involved and Defense Secretary Donald Rumsfeld said the United States had yet to decide if bin Laden was to blame.
Fears the terror could continue were stoked on Thursday when officials at New York's Kennedy Airport -- opened for business after being closed for two days -- arrested one person carrying false identification and detained "five or six" others.
Police Commissioner Bernard Kerik told a news conference that some of those detained were Arabs, and that the arrested man attempted to clear security with false identification and a pilot's license.
Attorney General John Ashcroft said later that officials did not believe other attacks were imminent.
Tuesday's attack -- relived repeatedly on video as television networks went to 24-hour news coverage -- sent two passenger planes smashing into the World Trade Center's twin towers, which later collapsed.
One other passenger jet was sent hurtling into the Pentagon, the nerve-center of the US military, and a fourth crashed in Pennsylvania after passengers, told of the earlier attacked, apparently sought to resist the hijackers.
Officials said they had located the black box flight recorder from this flight, which might provide valuable new evidence of the events aboard. Officials said they also believed they were zeroing on a black box in the Pentagon wreckage.
In Washington, Ashcroft told reporters that officials believed they had identified at least 18 hijackers, all of whom had tickets as passengers, who comandeered the four planes.
He added that the hijackers were believed to have a "significant" number of associates presumably still at large.
Calling the attacks the start of "the first war of the 21st Century," an emotional President Bush said the United States and its allies were ready to "whip terrorism" and declared on Friday a national day of mourning for the victims.
He planned to visit New York that day to support the thousands of volunteers risking their lives to help others in an extraordinary outpouring of heroism by ordinary people.
Defense officials, promising a "sustained engagement" against extremist forces, sent military aircraft into the skies over Washington DC and seven other cities, and officials said Rumsfeld was considering calling up thousands of military reservists to help maintain security and join active military units being prepared for possible relatiatory strikes.
In New York, Mayor Rudi Giuliani said the situation around the devastated high-rise was "horrible and gruesome."
"I'm sorry that I have to describe it that way, but that's unfortunately the situation that we're facing," he said, adding that 4,763 people were missing from the twin towers.
While the official death toll from the World Trade Center rose to 94, officials said body parts were being recovered and ordered more than 6,000 body bags. Around 3,800 were injured.
Outside hospitals, desperate people clutching pictures of friends and loved ones gathered in hopes of locating some of those still missing. Buildings across the city were heavily guarded by security staff, and police said there had been about 90 different bomb scares since Wednesday night -- including one that evacuated the Empire State Building.
At the attack site, rescue work in the hellish ruins was hampered as authorities kept a wary eye on One Liberty Plaza, which was feared unstable after sustaining damaged in Tuesday's attack on the the huge commercial complex.
"It is a fight," said Joe Allbaugh, director of the Federal Emergency Management Agency. "The rescue workers are putting their lives on the line. Time is not on our side."
But renewed hope swept through exhausted rescue teams after word that five firefighters had been pulled alive from the wreckage of towers where 40,000 people once worked. There were conflicting reports as to whether they had been buried in the initial collapses or had been trapped since then.
The nation's air transport system slowly began resuming operations, although with severe new security measures in place and warnings of long delays. German shepherd dogs patrolled at one airport and officials put an end to such conveniences as driving up to terminals in passengers cars and checking baggage at the curb.
But air traffic around the world remained in chaos, with thousands of passengers stranded at European airports. Several flights bound for the United States were forced to turn back Thursday after US authorities said no foreign-flagged carriers would be allowed to land at US airports.
Arab-Americans feared backlash attacks and reports of vandalism, threats and other kinds of intimidation surfaced coast to coast as the investigation pointed toward a Middle East connection.
One Muslim woman in suburban Chicago said she, her husband and their eight children endured a night of terror. "We had people riding up and down our block shouting obscenities. 'Go home you bleeping ragheads, bleeping a-rabs, we're gonna get you,'" said the woman.
ECONOMIC IMPACT FEARED
Economic fears were also increasing as US stock markets remained closed and New York's financial district lay stricken. Central banks declared themselves ready to defend their currencies, and US Treasury Secretary Paul O'Neill declared himself confident in the US economy.
Equity markets faced a third straight day of paralysis, the longest shutdown since World War One. Trading in Treasury bonds resumed but was thin with many traders unable to see prices once provided by firms in the destroyed World Trade Center.
Central banks worked together to inject $120 billion into the global financial system to help it beat back fears of a global recession, and expectations grew that the US Federal Reserve might cut interest rates soon -- by as much as a half a percentage point -- to bolster the world's richest economy.