Europe's leaders will fully back any military action by the US, according to EU Foreign Policy Chief, Javier Solana.
He said: "A military strike, if it is necessary, would be accepted by 100% of European leaders."
In an interview for BBC Television's HARDtalk, he dismissed fears about the solidarity of the European coalition.
And he refused to be drawn on whether the EU would go as far as supporting a US-backed assassination attempt, adding that it was not an issue up for discussion at the moment.
Mr Solana, Nato's former Secretary-General, also added that Europe would not be writing a blank cheque to help finance any military strike.
He said: "Nobody is going to ask us for a blank cheque and we would never give a blank cheque to anyone
"But the American people, its government and its institutions know they can count on the European people, the European institutions and the European governments."
Mr Solana said Europe was against terrorism, not against Islam, explaining: "I don't think this is a battle against a group of countries, against Islam or against a civilisation.
"It is a coalition between many countries, which belong to several civilisations, against terrorism."
He denied that disagreements with the Bush administration over issues such as Kyoto posed a threat to the solidarity of the alliance, adding that there were enough similarities between Europe and the US for them to work together in the fight against terrorism.
"There are things here that are very fundamental to our values and things that are secondary."
The final bill was not a consideration either. He said: "The cost of terrorism is very, very high and therefore the cost of fighting terrorism is high, but in the end we will not have terrorism."
Mr Solana said he shared the view of the UK Prime Minister, Tony Blair, that helping the USA was "a moral obligation".
He denied that Europe was guilty in the past of turning a blind eye to other humanitarian abuses such as Chechnya.
He also said that "concerted" pressure was being applied to resolve the situation in the Middle East, adding that he had been speaking regularly to all the main players.
Asked if he thought the ceasefire there would last, he replied: "I hope so ... I think it will.
"I think the situation in the world today is different to a month ago."
He said that people were responding to a new situation "which would without a doubt make everyone think."