From staff and wire reports

New York - In the most devastating terrorist onslaught waged against the United States, knife-wielding hijackers crashed two airliners into the World Trade Center on Tuesday, toppling its twin 110-story towers.

The deadly calamity was witnessed on televisions across the world as another plane slammed into the Pentagon and a fourth crashed outside Pittsburgh.

“Today, our nation saw evil,” President Bush said in an address to the nation Tuesday night. He said thousands of lives were “suddenly ended by evil, despicable acts of terror.”

Adm. Robert J. Natter, commander of the U.S. Atlantic Fleet said, “We have been attacked like we haven’t since Pearl Harbor.”

About 8:45 a.m., a hijacked airliner crashed into the north tower of the trade center.

Clyde Ebanks, an insurance company vice president, was at a meeting on the 103rd floor of the south tower when his boss said, “Look at that!” He turned to see a plane slam into the other tower.

The enormity of the disaster was just sinking in when 18 minutes later, the south tower also was hit by a plane.

At 10:05 a.m. the south tower of the World Trade Center collapsed and only 23 minutes later, the North Tower collapsed as if it were being peeled apart, releasing a tremendous cloud of debris and smoke.

Establishing the death toll could take weeks. The four airliners alone had a total of 266 people aboard and there were no known survivors.

And about 9:30 a.m., an airliner hit the Pentagon.

“There was screaming and pandemonium,” said Terry Yonkers, an Air Force civilian employee at work inside the building.

Later at the Pentagon, the symbol and command center for the nation’s military force, one side of the building collapsed as smoke billowed over the Potomac River. Eight hundred people are believed dead.

The military increased security across the country to the highest levels, sending Navy ships to New York and Washington to assist with air defense and medical needs.

Emergency Medical Service worker Louis Garcia said initial reports indicated bodies were buried beneath the two feet of soot on streets around the trade center.

“A lot of the vehicles are running over bodies because they are all over the place,” he said.

National Guard member Angelo Otchy of Maplewood, N.J., said, “I must have come across body parts by the thousands. I came across a lady, she didn’t remember her name. Her face was covered in blood.”

By evening, huge clouds of smoke still billowed from the ruins. A burning, 47-story part of the World Trade Center complex - already evacuated - collapsed in flames just before nightfall.

President Bush asked the nation to find comfort in Scripture as he mourned the deaths of thousands of Americans.

Bush spoke from the Oval Office just hours after bouncing between Florida and air bases in Louisiana and Nebraska for security reasons.

With smoke still pouring out of rubble in Washington and New York, Bush said, “These acts shattered steel, but they cannot dent the steel of American resolve.”

He spoke for fewer than five minutes from the desk presidents Bill Clinton and John F. Kennedy used before him. Beside the door, a TelePrompTer operator fed Bush the words that he and his speechwriters hastened to pen just an hour earlier.

U.S. officials began piecing together a case linking Osama bin Laden to what is being considered the worst terrorist attack in U.S. history. Investigators have been looking at information attained in an intercept of communications between his supporters and harrowing cell phone calls from passengers aboard the jetliners before they crashed.

A passenger on United Airlines Flight 93 called on his cell phone from a locked bathroom and delivered a chilling message. “We are being hijacked, we are being hijacked!” Minutes later the jetliner crashed in western Pennsylvania with 45 people aboard.

Afghanistan’s Taliban rulers condemned the attacks and rejected suggestions that bin Laden, who has been given asylum in Afghanistan, could be behind them.

“It is premature to level allegations against a person who is not in a position to carry out such attacks,” said Abdul Salam Zaeef, the Taliban ambassador in Pakistan. “It was a well-organized plan and Osama has no such facilities.”

Explosions resounded north of Kabul, Afghanistan, near its airport early today, but the United States quickly denied any involvement.

The explosions came in rapid succession, making buildings shudder.

“In no way is the United States government connected to those explosions,” said Defense Secretary Donald Rumsfeld.

A U.S. official, speaking on condition of anonymity, said the fighting in Kabul appeared to be rocket attacks by opposition rebels in response to the attack on rebel general Ahmed Shah Massood on Sunday. The insurgents blamed the attempt on the ruling Taliban, a hard-line Islamic group.

An opposition spokesman denied the rebels were responsible for the violence and a Taliban spokesman blamed the explosions on a fire at an ammunition depot.

Bush said in his address that the United States would be against “those behind these evil acts.”

“We will make no distinction between the terrorists who committed these acts and any country that harbors them,” he said.