Europe ground to a halt for three minutes at noon yesterday as thousands of people stood in silence to remember the victims of Tuesday's attacks in New York and Washington.
In a joint statement, EU leaders promised to make their common security and defence policy operational as soon as possible and to create a European warrant for arrest and extradition.
Ireland was the only EU member-state to declare yesterday a public holiday, but acts of remembrance took place throughout the Union.
In Brussels, thousands of people joined Belgium's Prime Minister, Mr Guy Verhofstadt, and the Commission President, Mr Romano Prodi, at a roundabout in the centre of the city's European quarter.
The district was sealed off as the EU officials stood in silence while a church bell tolled faintly nearby.
A separate ceremony was held at NATO's headquarters a few kilometres away.
The Paris Metro stopped for three minutes, and President Jacques Chirac led a ceremony in the courtyard of the Elysee Palace.
An estimated 200,000 people joined political figures in Berlin at a sombre memorial service to the victims of Tuesday's suicide attacks.
Chancellor Gerhard Schroder, members of his Social Democrat-Green cabinet, and opposition leaders gathered and stood silently by Brandenburg Gate to hear the addresses of President Johannes Rau and America's ambassador, Daniel Coats.
"Nobody knows more than the people of Berlin what America has done for freedom and democracy in Germany," Mr Rau said. "We would not be able to stand here tonight without their support through the years and through tough times."
The towering gate was a poignant backdrop for the memorial service, as it stood in the no man's land between communist east and capitalist west before Germany was reunited.
Thousands of Germans, many in tears, have placed flowers in front of the American embassy in Berlin and consulates around the country.
Across the continent, television and radio programmes were halted for three minutes, to be replaced by sombre music and images of Tuesday's horror.
Pope John Paul interrupted his routine activity on Friday to join the world in commemorating the victims of the terror attacks in the US.
The Vatican said that at noon the 81-year-old Pope went to his private chapel in the papal summer residence at Castelgandolfo, south of Rome.
"He retreated into silent prayer for the victims of the terror attacks that struck the United States last Tuesday and to implore comfort for the injured and for reconciliation and peace in the world," spokesman Mr Joaquin Navarro-Valls said.
The Pope was extremely shaken by the attacks, which he has called a "dark day in the history of humanity".
He has urged the world not to allow a "spiral of hate and violence" to prevail.
In Sarajevo, local residents laid flowers and candles outside the US embassy.
The EU leaders declared that Washington could depend on their solidarity and full co-operation to ensure that justice is done.
"We will not, under any circumstances, allow those responsible to find refuge, wherever they may be.
"Those responsible for hiding, supporting or harbouring the perpetrators, organisers and sponsors of these acts will be held accountable," they said.
The EU would commit itself to defend justice and democracy at a global level and, the leaders said, they would continue to develop the Common Foreign and Security Policy.
The leaders said they would accelerate the implementation of a European judicial area, which would entail the mutual recognition of legal decisions and verdicts.
"Our citizens will not be intimidated. Our societies will continue to function undeterred.
"But today our thoughts are with the victims, their friends and the American people," the EU leaders declared.
