This battle will take time and resolve, but make no mistake about it, we will win

President Bush

Nato ambassadors invoked a mutual defence clause in the organisation's founding treaty for the first time in its history. It envisages a collective response to armed attack against one of its members.

"Accordingly, the United States' Nato allies stand ready to provide the assistance that may be required as a consequence of these actions of barbarism," a statement by the Nato council said.

FBI Director Robert Mueller told a news conference that several of the hijackers as well as possible associates still in the US had been identified.

US Attorney General John Ashcroft said some of the hijackers had trained as pilots in the United States.

And in other developments during the day:

• Secretary of State Colin Powell said that both the White House and the presidential jet, Air Force One, had been targeted in the attacks. This appeared to explain Mr Bush's delay in returning to Washington on Tuesday.

• Commenting on what he described as the biggest investigation ever conducted by the Justice Department, the US attorney-general said between three and six individuals were involved in the hijacking of each plane.

• After a day of highly volatile trading, European shares seized back some of the ground lost during Tuesday's turmoil. US markets reopen on Thursday.

• International flights are subject to severe disruption, and US air space is still closed to civilian flights. Transport Secretary Norman Mineta is said to be hoping to resume civilian flights on Thursday.

• The recovery of bodies from the rubble of the World Trade Center was disrupted by the collapse of a seven-storey building which used to link the giant twin towers.

Death toll

All 266 on board the four planes are feared dead Between 100 and 800 are believed to have died at the Pentagon. No survivors yet found 41 people are known to have died so far in the WTC. Four people have been pulled alive from the rubble. A few thousand were estimated to be inside the buildings when the first plane crashed At least 259 uniformed service members are missing in the WTC, feared dead

But Mr Bush said that it was definitely not business as usual in the US administration, and that everyone was operating on heightened security alert.

"This morning I am sending to Congress a request for emergency funding so we can spend whatever it takes to rescue victims... and to protect national security," he said.

Two hijacked planes crashed into the towers of New York's World Trade Center, triggering explosions and fires that resulted in their collapse.

A third hit the Pentagon in Washington, causing a fire and between 100 and 800 casualties.

A fourth hijacked passenger jet crashed in Pennsylvania, south-east of Pittsburgh, with all 45 people on board feared dead.

Suspects

FBI agents were investigating evidence that suspected sympathisers of Saudi dissident Osama Bin Laden were operating in Broward County and Daytona Beach in the state of Florida.

Also, a report in the Boston Herald said that authorities in Massachusetts had identified at least five Arab men as suspects in the attacks launched from Logan International Airport.

Officers are said to have seized a car laden with Arabic-language flight training manuals from the central parking garage.

The Boston Globe said that the luggage of one of the men, who arrived in Boston on another flight, had been found after it missed his connection.

It contained a Koran, an instructional video on flying commercial airliners and a fuel consumption calculator.

There were also reports that the hijackers were able to do what they did by smuggling shaving kits containing knife-like weapons aboard the planes.

Conversations intercepted

"Everything is pointing in the direction of Osama Bin Laden", Republican Senator Orrin Hatch said.

Bin Laden: Most wanted terrorism suspect

He added that US intelligence had intercepted conversations between Bin Laden supporters discussing Tuesday's attacks and acknowledging that targets had been hit.

However Afghanistan's ruling Taleban - on whose territory Mr Bin Laden lives - rejected the idea that he could have been involved.

BBC world affairs editor John Simpson said Mr Bin Laden undoubtedly had the capabilities to have carried out the attack.

He said Mr Bin Laden had 2,000 men in training camps in Afghanistan, most of them Arabs from countries like Algeria and Saudi Arabia and Egypt.