Security is being tightened at airports and railway stations across Europe after explosions attacked London's transport system on Thursday.
European Union Justice Commissioner Franco Frattini is reportedly to have called on Europe to offer Britain all the help it needed.
European Union Justice Commissioner Franco Frattini called on Europe to offer the UK all the help it needed. .
Hours after the attacks, Belgian authorities met to discuss security measures in Brussels, also home to a number of EU institutions and NATO, according to British Broadcasting Corporation (BBC).
Belgian Prime Minister Guy Verhofstadt later said there was no evidence that Belgium was at a higher risk, but extra security precautions would be taken on trains and subway stations and at border checkpoints, airports and seaports.
Spain, the target of terror attacks which killed 191 people in Madrid on 11 March last year, raised its security standing to the highest level.
This level of alert involves the mobilization of the security forces to keep watch and protect places with large amounts of people as well as strategic sites needed for normal citizen activity, the interior ministry said.
French Prime Minister Dominique de Villepin announced France's step up to red alert - the second-highest level of security.
Security is especially tight for rail passengers travelling between Paris and London. Eurostar trains are still running but the company has advised people not to travel to London.
Italian Interior Minister Giuseppe Pisanu told the Senate, "The level of alert has been raised in Italy as in all the other European countries."
Dutch Prime Minister Jan Peter Balkenende said security would be stepped up at the Dutch borders and around British sites in the Netherlands.
Other countries paid tribute to the victims of the attacks.
Russia, the Czech Republic, Hungary and Romania are also said to have raised their security levels.