Londoners pause in central London's Tavistock Square, site of bombed No. 30 bus one year ago, in London, Friday

Britain has commemorated the first anniversary of the terrorist bombings that killed 52 passengers and wounded 700 more on London's mass transit system.

Government officials and relatives of the victims have laid floral wreaths, dedicated plaques and attended religious services in remembrance of those killed and wounded in the attacks carried out a year ago by four British Muslim men. At midday, Queen Elizabeth led a two-minute silence across the kingdom.

Commuters and workers stand outside King's Cross Station in London

As the ceremonies proceeded, millions of commuters traveled as normal Friday on the capital's bus and subway network.

London's police chief, Ian Blair, spoke on British radio about the events of one year ago, and he warns that the terrorist threat has not diminished.

"The threat is very grim, there's no doubt about it," he said. "I mean, there are as we speak, people in the United Kingdom planning further atrocities."

Police say they have interdicted three other terrorist conspiracies in the past year, and 70 anti-terrorist investigations are currently under way.

Police Commissioner Blair says Londoners must carry on as normally as possible, while police try to increase their ability to gather intelligence and build public confidence.

"The first thing to do is just get on with their lives," he said. "I mean, we must not let the terrorists win under any circumstances by changing and being fearful. But secondly, the great endeavor of the Metropolitan Police at this time is the roll out of community policing which we are putting into every ward across London during the course of this year."

Adding to the tension of the anniversary, a video was broadcast Thursday on which one of the bombers said more attacks are coming. The video was of Shehzad Tanweer, a British-born Muslim of Pakistani decent. He said Britain will be vulnerable to attacks until it withdraws troops from Afghanistan and Iraq, and ends support for the United States and Israel.

The video contains segments of al-Qaida leader Osama bin Laden and his deputy, Ayman al-Zawahiri. Al-Qaida has claimed responsibility for the bombings before, but police say they have not determined who was behind the attacks.