British police have released video footage showing the London subway suicide bombers on a reconnaissance trip less than two weeks before the July 7 blasts that killed 56 people.

Scotland Yard says the closed circuit television recordings show three of the four bombers traveling through London on June 28, making the same journey they did on the day of the bombings. Officials believe they were checking out potential targets on the London transport system and checking how long the journey would take on the day of the attack.

The development comes one day after al-Qaida's number two leader, Ayman al-Zawahri, said the terror network was behind the bombings. In a video broadcast on Arabic language al-Jazeera television, he said the bombings were aimed against what he termed as British aggression against Muslims and its part in creating Israel.