National News

The craft struck the five-sided structure with tremendous force, driving itself through the huge outer rings of the Pentagon and into the park-like central courtyard.

Glenn Flood, a Pentagon spokesman, told The Associated Press that there were "extensive casualties and an unknown number of fatalities."

"We don't know the extent of the injuries," he said.

President Bush was in Florida when he got word of the attacks on the World Trade Center and the Pentagon. "Terrorism against our nation will not stand," he said before he was flown to the safety of a military base in Louisiana.

Vice President Dick Cheney was in Washington and was taken, along with the first lady, Laura Bush, to an undisclosed secure location. Security was tightened around other government leaders as well. Defense Secretary Donald Rumsfeld was not hurt, Flood said. Nor apparently was Gen. Richard Myers, the incoming chairman of the Joint Chiefs of Staff. The present chairman, Gen. Henry H. Shelton, was out of town.

The crash was accompanied by a thunderous explosion that virtually collapsed one side of the gray structure, a symbol of America's military might for more than a half-century. To enemies of America, it is also the symbol of what they see as U.S. imperialism.

Many Pentagon employees told of being knocked out of their chairs by the explosion. Moments afterward, they began evacuating the building, and streams of people in white, blue and green uniforms mingled among others in civilian clothes. More than 20,000 military and civilian employees work at the defense center, which is in Arlington, Va., just across the Potomac River from the capital.

The craft that crashed into the building was an airliner, which witnesses said accelerated as it approached the building.

American Airlines confirmed at midmorning that it had lost two aircraft with a total of 156 people aboard, one a flight from Boston to Los Angeles, the other a plane leaving Washington's Dulles Airport for Los Angeles.

An initial report of a car bomb exploding outside the State Department Building in northwest Washington, just a short distance from the National Mall and the Lincoln Memorial, was later determined to be false.

The Pentagon blast brought a quick evacuation of the White House, where television reports said in mid-morning that a separate bomb threat had been received. The Capitol, the Supreme Court and virtually all other government buildings were shut down, except for those that are headquarters to law enforcement agencies, where command centers were being set up.

The Pentagon attack, quickly following on the horror at the World Trade Center, brought the government to a standstill. All the talk of tax cuts and budget deficits that had filled Washington corridors before Tuesday suddenly seemed irrelevant.

Bush called the events an apparent "terrorist attack" and pledged that the federal government would "hunt down" those responsible.

By midday, investigations were already under way to try to establish responsibility for possible lapses in airport security and for what might be a failure of intelligence, since Tuesday's attacks were evidently coordinated and caught the country by surprise.

The terrorist attacks were certain to accelerate debate about how the United States should deal with threats from within the country and abroad.

The events at the World Trade Center and the Pentagon stunned official Washington as few events have in recent times. The effect was likened by some to the attack on Pearl Harbor or the assassination of President John F. Kennedy. The deadly bombing in Oklahoma City in 1995 seemed eclipsed by what happened on Tuesday.

Early suspicions about Tuesday's attacks focused on Osama bin-Laden, the Saudi tycoon who has avowed his hatred for the United States.

By early Tuesday afternoon, some three hours after the Pentagon attack, flames were still streaming from the building's windows. Secondary explosions were reported, and great billows of smoke continued to drift into the clear blue sky.

The Pentagon, completed in the 1940s, is one of the biggest office buildings in the world. Its interior is a maze of corridors and hallways. Each of the sides is so huge that only a large and powerful object traveling at great speed could push itself from the exterior of the building into the courtyard.

The explosions and subsequent government shutdowns plunged the District of Columbia into severe gridlock as government employees tried to make their ways home. There was no panic in the streets, but the wail of police sirens was constant, and people gathered in knots to ask questions and share snippets of information and rumors.

More than a dozen fire engines could be seen around the White House. There was no access to Lafayette Square across Pennsylvania Avenue, which was being guarded by officers with sub-machine guns.