The US launched an international diplomatic counter-offensive last night against those responsible for the devastating attacks on Tuesday which the Bush administration regards as an act of war against the US.
President Bush aims to build a global coalition against terrorism and last night won endorsement from the North Atlantic Treaty Organisation.
Earlier, he conferred with the leaders of the five permanent members of the UN Security Council and made clear he wanted the attacks punished in kind.
The US has now set out to give such probable retaliation as much legitimacy as possible.
As Mr Bush's strategy was emerging in Washington, rescuers in New York were trying to cope with the enormity of a rescue and clean-up operation in which there was fading hope of finding many survivors. Only four people were found alive by late yesterday.
A huge swathe of southern Manhattan has been turned into a dust-laden wasteland. Where the 110-storey twin towers of the World Trade Centre stood is now a heap of rubble in which thousands of people are entombed. Late last night, what remained of the twin towers - the bottom seven floors - collapsed and rescue efforts were suspended, dashing hopes of finding further survivors. Another building, One Liberty Plaza, was also beginning to collapse.
The city's mayor, Mr Rudy Giuliani, said last night only that 55 bodies had so far been recovered. One finance company in the Centre is missing some 2,500 employees. Around 800 people are believed to have died at the Pentagon in Washington.
In Dublin, the Department of Foreign Affairs said it expected "quite a number" of Irish casualties. Last night, the family of an Irish labourer, Mr Kieran Gorman, from Lavagh in Co Sligo, who had been working in the Centre, confirmed that he was missing.
Concerns were growing for several other missing Irish people - among them two first cousins of the Fine Gael TD, Mr Gerry Reynolds - and scores of Irish-Americans are also feared dead among the New York fire fighters and police who lost their lives when the twin towers collapsed.
The Government has declared tomorrow a national day of mourning. All public offices and schools are expected to close. Similar gestures have been made by other EU governments.
A huge FBI manhunt gathered pace in the US yesterday with police raids in Boston and Florida. The hijacker's car was found at Boston airport, together with a flying manual in Arabic. Investigators believe the pilots may have been trained in the US.
It emerged yesterday that the plane which crashed into the Pentagon had initially been on a course aimed directly at the White House and Air Force One, President Bush's jet.
Passengers of the fourth of the hijacked planes, which crashed in woodland near Pittsburgh, may have staged a revolt against their captors.
According to CNN, one of the passengers on a mobile phone was told of the two planes crashing into the Centre in New York. He apparently consulted other passengers who decided to take on their captors.
In his toughening stance, President Bush received swift support from both the UN Security Council and NATO.
NATO invoked Article five of its treaty to declare that the attack on the US had been an attack on all alliance members.
The UN Security Council backed the President, saying it would combat terrorism "by all means".
A shocked US began a phased return to work as its people wait nervously for a tally of the dead. Police raids in Boston and Florida began the process of picking up the traces of those responsible for the attacks.
Intelligence sources in the US are also confirming that radio intercepts after the attacks have added to a growing conviction the Saudi millionaire, Mr Osama bin Laden.
NATO's action of invoking Article five for the first time in its history, opens the way for a possible collective military response.
"The (NATO) Council agreed that if it is determined that this was an attack directed from abroad against the US, it shall be regarded as an action covered by Article five of the Washington Treaty, which states that an attack against one ally is an attack against them all," its Secretary-General, Lord Robertson, told reporters.
The article commits each of the 19-member nations to take "such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area".
With flags flying at half-mast, the Security Council condemned the attacks and called on the world to help find the perpetrators and those who sheltered them.
It "expressed its readiness to take all necessary steps to respond to the terrorist attacks of September 11th 2001 and to combat all forms of terrorism".
After a minute of silence, each of the 15 members of the UN Security Council, including Ireland's representative, Ambassador Richard Ryan, spoke individually. They then rose as a group rather than voting from their seats to adopt its resolution.
Speaking to journalists the US Secretary of State, Mr Colin Powell, welcomed both decisions and called for all nations to join a worldwide coalition against terrorism. It would be a key priority of the Administration.