The US's allies in Europe tightened security measures yesterday as the military strikes in Afghanistan stoked fears of retaliatory attacks.
In Washington, the US State Department warned that the attacks "may result in strong anti-American sentiment and retaliatory actions against US citizens and interests throughout the world."
It said any US civilians now in Afghanistan should leave the country immediately and that Americans in other parts of the world should "monitor the local news, maintain contact with the nearest American embassy or consulate and limit their movement in their respective locations."
Italy's Prime Minister, Mr Silvio Berlusconi, put the country on a state of alert shortly after US and British forces unleashed attacks on Afghanistan, his office announced.
Mr Berlusconi set up a crisis cell, comprising officials from the defence, interior and foreign ministries, under the command of an Italian general. "All the security measures that have been in place recently have been reinforced. They concern not only those frequented by American citizens in Italy, but everyone, all sensitive targets like the airports, subways, etc," a spokesman for Berlusconi's office said.
Italian television showed troops putting concrete barriers at the entrance to a major NATO base in Naples, one of several alliance facilities in the country.
Increased security measures were also put in place for government buildings in Britain, Washington's closest ally, police said.
A spokeswoman for London's Metropolitan Police said security was being stepped up in the capital, while appealing for people to go about their business as normal.
"High visibility policing will continue and additional security is also being introduced to potentially vulnerable areas where needed," said the spokeswoman, without giving more details.
In Berlin, additional police forces were sent to embassies of several Western governments in the city, including those of the US, Britain and France, as well as to other "especially vulnerable" buildings, he said.
Turkey stepped up security around diplomatic buildings of fellow NATO members.
A crisis centre has been set up by Interior Minister Mr Rustu Kazim Yucelen, who ordered security measures to be tightened around airports and public buildings.
France instituted its high-alert "Vigipirate" security measures shortly after the September 11th attacks, which include increasing the number of police on the streets and having armed soldiers patrolling with police in airports, railway stations and outside vulnerable buildings.
On Friday it made public security plans aimed at tackling any biological or chemical attacks.
Officials in Moscow said they were tightening security around the US and British embassies and other key facilities following the US-led attacks.
The officials said security measures were being increased in the city's subway, at train stations and airports as well as around power plants.