Britain came to a standstill Friday to mark the first anniversary of the London transit suicide bombings that killed 52 people and wounded 700 others.
Queen Elizabeth and Prime Minister Tony Blair led a nationwide two-minute period of silence at midday to honor the victims of the July seventh, 2005 attacks.
Standing with emergency service workers in London, Mr. Blair said the country is united across racial and religious divides as people mourn the victims of the bombings.
Ceremonies also were held at King's Cross subway station, where the first of three bombs detonated in the London Underground, and at Tavistock Square, where a fourth suicide bomber destroyed a double-decker bus.
Memorial plaques were unveiled at the locations where the bombs detonated.
The head of London's Metropolitan Police, Ian Blair, said the threat of terrorism has not diminished. He described the situation as grim.
A video was broadcast Thursday of one of the four suicide bombers who said the 2005 bombings were only the beginning of such attacks.
Suicide bomber Shehzad Tanweer said the attacks will continue until Britain ends involvement in Afghanistan and Iraq, and stops financial and military support for the United States and Israel.
Public opinion polls also indicate evidence of rising mistrust in Britain's Muslim community of police and the political establishment.