French and Italian officials have raised terror alert levels in their countries as others express support for the British people.
The French government raised the country's terror alert level to the second-highest rating following a series of explosions in London.
After announcing the alert escalation, Prime Minister Dominique de Villepin expressed support for the British people. President Jacques Chirac in Scotland for the Group of Eight Summit told British Prime Minister Tony Blair that he had France's "total solidarity."
Italian security officials have raised alert levels at the country's airports to the maximum. In Rome, the European Union's commissioner for justice and security affairs Franco Frattini called the London blasts terrorist attacks.
The secretary-general of NATO condemned what he called "heinous crimes" on London and called for unity in the fight against terrorism.
Officials in Washington have boosted security in the capital's subway system, but the U.S. Department of Homeland Security kept the terrorism alert level steady and said there is no indication of a threat of similar attacks against the United States.
Some information for this report provided by AFP, AP and Reuters.