The Government has agreed to allow US forces engaged in a military response to last week's terrorist attacks in America to refuel at Irish airports and fly over Irish airspace, the Taoiseach announced last night.
Speaking in Brussels during an emergency EU summit, Mr Ahern said the US was entitled to launch military action without a fresh mandate from the United Nations.
The Minister for Foreign Affairs, Mr Cowen, will make the offer to the US Secretary of State, Mr Colin Powell, when they meet in Washington next Wednesday.
"We will make it clear that if they want to use our facilities, they can," the Taoiseach said.
A Government spokesman confirmed last night that permission to refuel in Ireland could extend to armed warplanes as well as to troop carriers. But the Taoiseach ruled out the involvement of Irish soldiers in any US-led operation.
"We will stick to our traditional position on that," he said.
Mr Ahern said last week's UN resolution condemning the attacks in New York and Washington had confirmed the right of the US to act in self-defence under Article 51 of the UN Charter.
"The UN has played its role," he said.
The EU leaders issued a strong expression of solidarity with the US and promised their support for a military response. In a joint statement after the meeting, they promised to co-operate with Washington in bringing the perpetrators of last week's attacks to justice.
"On the basis of Security Council Resolution 1368, a riposte by the US is legitimate. The member-states of the Union are prepared to undertake such actions, each according to its means. The actions must be targeted and may also be directed against States abetting, supporting or harbouring terrorists. They will require close co-operation with all the member states of the European Union," the statement said.
An earlier draft of the statement said all EU states would take part in a US action but the text was changed when the French President, Mr Jacques Chirac, pointed out that four EU states were not members of a military alliance.
The leaders approved a plan discussed this week by EU justice and home affairs ministers to improve co-operation in combating terrorism. The measures include the creation of a European arrest warrant, obliging police in all 15 EU states to pursue suspected terrorists wanted in any member-state. Extradition for terrorist offences would become automatic between member-states.
The EU hopes to agree a common definition of terrorism but the Taoiseach acknowledged that the Government needed to study the proposed definition to ensure it was consistent with Irish law.
The proposed framework has a broad definition of international terrorism that includes activities aimed at "seriously altering the political, economic or social structures" of more than one country.
EU leaders stressed that the campaign against global terrorism was not a war against Islam and expressed the hope that Arab states would join the international coalition. The German chancellor, Mr Gerhard Schroeder, insisted that most Muslims were as outraged as everyone else by the attacks.
The leaders agreed the EU's foreign policy chief, Mr Javier Solana, the External Affairs Commissioner, Mr Chris Patten and Belgium's foreign minister, Mr Louis Michel, should travel to the Middle East next week to help build the international coalition.
Afghanistan's Taliban government yesterday rejected President Bush's demand that Osama bin Laden be handed over without further ado.
In Pakistan, tensions are continuing to rise. Yesterday thousands of angry people took to the streets in protest at the decision of the leader, Gen Pervez Musharraf, to side with the US.
At least three people were shot dead and three others were injured during violent protests in the commercial capital, Karachi. Gunfire erupted at a rally after Friday prayers in one area.
Weekend developments will be reported by The Irish Times website, www.ireland.com, on the Breaking News Service. The full text of President Bush's speech may also be read there.