News of the World Trade Centre and Pentagon attacks brought shocked reactions around the world, including from the Middle East, where most analysts located the likely origin of the events.

US President George W. Bush described the attacks as a "national tragedy" and said from Florida that the full resources of the US would be used to "hunt down" the perpetrators.

Rudolph Guiliani, mayor of New York, described the scenes on the streets as "horrible" and said there would be many casualties. "We urge (people) to remain calm and stay in their home or their place of business. I have never seen anything like this. I saw people jumping out of the World Trade Centre. It is a horrible, horrible situation.

"Right now we have to focus of saving as many people as possible."

Mr Guiliani said the National Guard had been alerted and was likely to relieve emergency service teams working to evacuate people from the area.

From Gaza, Palestinian president Yassir Arafat said: "I send my condolences, the condolences of the Palestinian people, to American President Bush and his government and to the American people for this terrible act."

"We completely condemn this serious operation... We were completely shocked. It's unbelievable, unbelievable, unbelievable," Mr Arafat told reporters.

Shortly after the World Trade Centre attacks, the Democratic Front for the Liberation of Palestine claimed responsibility for the attack, but later denied any involvement.

Binyamin Ben-Eliezer, the Israeli defence minister, described the attacks as "simply a tragedy".

"I sympathise with the American people. It's simply a terrible thing," Mr Ben-Eliezer told Israel's Army Radio.

Tony Blair, UK prime minister, summoned senior cabinet ministers to an emergency security meeting after cancelling his speech to the Trade Union Congress conference in Brighton, scheduled for about the same time as the World Trade Centre explosions occurred, and returning to London.

Mr Blair described the attacks as "the most terrible shocking event" and offered his "deepest condolences" to the president and people of the US.

Such actions were the "new evil in our world today" and democracies had to "come together and fight it together and eradicate this evil completely from our world," he said.

Jack Straw, UK foreign secretary, offered to help the US government bring the perpetrators to justice.

"The world will be watching these pictures from the US with absolute horror. There can be no justification for these appalling acts of terrorism. Our hearts go out to the families of the victims of these atrocities," Mr Straw said in a statement.

"We in Britain have offered whatever help we can to the American government to bring the perpetrators to justice and I have passed my condolences to the US Secretary of State Colin Powell." Mr Powell was on a scheduled visit to Bogota, Colombia, at the time of the attacks but a spokesperson said he would be returning to the US as soon as possible.

Visiting Ukraine on behalf of the European Union, the Belgian Prime Minister Guy Verhofstadt and Deputy Prime Minister and Minister of Foreign Affairs Louis Michel have expressed their deep shock and dismay upon hearing of the attacks.

On behalf of the European Union, they condemned "the cowardly and barbaric attack on innocent civilians", offering their "sincerest condolences to the families of the victims and to the American people".

They reiterated their "outright condemnation of all forms of terrorism and their determination to combat it with every means at their disposal". They also stressed the "total solidarity" of the European Union with the American people at this difficult time.

Jacques Chirac, French president, condemned what he called the "monstrous attacks" in the US, and immediately cut short a trip to Brittany to return to Paris.

"It is with immense emotion that France has learned of the monstrous attacks that have just hit the US," Mr Chirac said. "In these terrible circumstances, the French people stand at the side of the American people."

He added: "I assure President George Bush of my total support. France has always condemned terrorism and condemns it now unreservedly."

Chris Patten, the European Commissioner for External Affairs, said from Brussels: "We are all watching events with absolute horror. Our prayers and deepest sympathies go out to our friends in the United States."

The European Central Bank declined to comment on the economic impact of the attacks but Wim Duisenberg, the bank's president, was still planning to address the European Parliament on Wednesday.