Even nations that have been at odds with the United States denounced the attacks.
North Korea called the attacks "very regretful and tragic," adding that it "is opposed to all forms of terrorism." The U.S. State Department lists North Korea among seven national "sponsors of terrorism."
Libya, Syria, Sudan and Iran all of which are accused by the United States of sponsoring terrorism also condemned the attacks.
"Irrespective of the conflict with America it is a human duty to show sympathy with the American people, and be with them at these horrifying and awesome events which are bound to awaken human conscience," Libyan leader Moammar Gadhafi said.
However, an Iraqi state-run newspaper described the attacks as due punishment. "Now, America is gaining the fruits of its worldwide crime," al-Iraq newspaper said Wednesday.
In the hours after the attack, Iraqi television played a patriotic song that began "Down with America!" as it showed the towers collapsing.
And in the West Bank city of Nablus, thousands of Palestinians poured into the streets to celebrate, chanting "God is Great" and distributing candy to passers-by, even as their leader, Yasser Arafat, expressed horror over the attacks.
"We are donating our humble abilities to (President Bush) and to the American people," Arafat said at Shifa hospital in Gaza City.
The European Union said it stood shoulder to shoulder with the United States, with some member states using their close ties to gently urge the world's superpower, in a grim mood for vengeance, to think calmly before it unleashed retaliation.
"In the darkest days of European history, America stood close by us and today we stand close by America," European Commission President Romano Prodi said.
"Nothing will ever be the same."
Europeans prepared to show their sympathy with America's as yet unquantified loss on a massive scale.
Brussels declared a European Union-wide day of mourning on Friday for the U.S. victims. Denmark was holding a national memorial service. Russia observed a minute's silence.
Poland called off rallies in an election campaign. European soccer came to a halt as a mark of respect.
"The 11th of September, 2001, will go down for us all as a black day in history," said German Chancellor Gerhard Schroeder.
Japan joined the chorus Wednesday when Prime Minister Junichiro Koizumi said he could not forgive the acts of terror.
The strikes on the World Trade Center and Pentagon were likened to Japan's attack on Pearl Harbor that sucked the United States into World War II, but Britain said the horror for Americans at home must be even greater.
"There has never been such a trauma in terms of casualties in the history of the United States since the Civil War in the middle of the 19th century," Foreign Secretary Jack Straw said before a crisis meeting with European counterparts.
U.S. President George W. Bush declared the attacks an "act of war."
Sensing the American rage, some allies called for restraint.
"It's not easy to warn the United States in such a situation," Norway's Foreign Minister Thorbjoern Jagland said, "(but) we must hope there won't be an irrational revenge."
Spain, the United Nations and others echoed his plea.
"The decision to hit back will be taken with circumspection because, in the job we do, one always has to think about the attack after that," French Defense Minister Alain Richard said.
"If an act of retaliation leads to a new destabilization, you haven't won anything at all."
No one has claimed responsibility but Saudi militant Osama bin Laden is the prime suspect of the United States, although he and the Afghan leaders who shelter him denied he was to blame.
Western aid workers and diplomats in Afghanistan began pulling out in case of U.S. strikes. The country's Taliban leaders said, as they have before, that they may consider bin Laden's extradition if proof of guilt is presented.
Sweden hoped the masterminds would face trial and feared the new world being shaped by the attacks would be a closed one.
"I am extremely worried that what has happened ... will result in a more closd world, that it will be more difficult for us to meet across borders," Prime Minister Goran Persson said.
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