We were all victims of this attack

Belgian Foreign Minister Louis Michel

In a declaration released after the meeting, the ministers asked all Europeans to observe the silence at 1000GMT (1100BST) on Friday.

"We were all victims of this attack," Belgian Foreign Minister Louis Michel told a news conference.

Earlier, European Commission President Romano Prodi told a news conference: "In the darkest days of European history America stood close by us and today we stand close by America.

"We will not allow terrorism to win the day, and we will not allow terrorism to guide the world," he added.

We are also ready to offer practical help, if necessary, for example with rescue operations and with helping to track down the perpetrators

Spokeswoman for Javier Solana

A declaration from the foreign ministers' meeting pledged full co-operation in combating terrorism, tracking down those responsible for the attacks and helping in search and rescue operations.

The EU, it said, would "spare no efforts to help identify, bring to justice and punish those responsible".

"There will be no safe haven for terrorists and their sponsors," it said.

The declaration said the EU would work closely with the US and "all partners" to combat international terrorism.

Rescue offer

Flags flew at half mast at EU headquarters, and on many buildings across Europe.

All European commissioners have been recalled to Brussels.

In the European Parliament, the chairman of the European Central Bank, Wim Duisenberg, said the bank had offered the US Federal Reserve "any necessary help".

Solana: Help for the 'battle against terrorism'

"I would like to emphasise the ECB and the national central banks are standing ready to support the normal functioning of markets and relevant operation systems if the need arises," he added.

The EU's foreign policy chief, Javier Solana, promised a strong message of support to the president and people of the United States.

"We are also ready to offer practical help, if necessary, for example with rescue operations and with helping to track down the perpetrators of these terrible acts," his spokeswoman, Cristina Gallach, said.

We are all agreed that this attack was a declaration of war on the free world

German Chancellor Gerhard Schroeder

Nato's Secretary-General George Robertson also attended the EU meeting.

"We stand together. We are two organisations with one voice, one strong voice, that we will not stand for this terrorism," he said.

Non-essential Nato staff were told to stay away from work on Wednesday.

'Declaration of war'

In Berlin, Chancellor Gerhard Schroeder told the lower house of parliament he had assured the US president of Germany's "unlimited" solidarity.

Lord Robertson: Told some staff to stay at home

He said he had talked to the French, Russian and British leaders, adding: "We are all agreed that this attack was a declaration of war on the free world."

UK Foreign Secretary Jack Straw said: "We are part of the same community... We can only defeat this kind of terrorism by much firmer, co-ordinated international action."

Diplomats noted that some EU members, such as the UK and Spain, had long experience of fighting militants who attack civilian targets.

The European Parliament's foreign affairs committee observed a minute of silence as a mark of respect for the victims of the US attacks.

European stock exchanges observed a minute's silence at 1245GMT.