Three men have been charged in connection with the 7 July suicide bombings in London.
The 7 July bombers attacked a London bus and three Tube trains
Mohammed Shakil, 30, Waheed Ali, 23, and Sadeer Saleem, 26, were charged with conspiracy to cause explosions on transport or at tourist attractions.
Scotland Yard said the hunt for those involved in the bombings was not over and more arrests were expected.
Four suicide attacks killed 52 people on three London Underground trains and a bus in 2005.
Mr Shakil, from Beeston, West Yorkshire, and Mr Ali, from Tower Hamlets, east London, who was previously known as Shipon Ullah, were boarding a flight to Pakistan at Manchester Airport when they were detained in March.
Mr Saleem, also from Beeston, was arrested at an address in Leeds.
The three are accused of conspiring with the 7 July bombers between the 1 November 2004 and the 29 June 2005 to cause explosions on the London transport system or at tourist attractions in the city.
"The allegation is that they were involved in reconnaissance and planning for a plot with those ultimately responsible for the bombings on the 7 July before the plan was finalised," said Sue Hemming, head of the Counter Terrorism Division of the Crown Prosecution Service.
Bombers Mohammad Sidique Khan, 30, Shehzad Tanweer, 22, Germaine Lindsay, 19, and Hasib Hussain, 18, all died in the blasts, and the latest charges are the first to be made over the attacks.
Deputy Assistant Commissioner Peter Clarke, head of Scotland Yard's Counter Terrorism Command, said police had taken 15,000 statements and followed 19,000 leads during its 21-month investigation into the "murder of 52 innocent victims".
"I appreciate that bringing these charges will have an impact on many people," he said. "For some it will bring back horrible memories of that terrible day.
"For others there may be some relief that after such a length of time there is some visible progress in an investigation that has had to be kept secret."
More arrests 'likely'
He went on to appeal for more people, especially from West Yorkshire, to come forward to help with the investigation.
"I firmly believe that there are other people who have knowledge of what lay behind the attack in July 2005 - knowledge that they have not shared with us, in fact I don't only believe it, I know it for a fact."
Mr Clarke said the police particularly required information about the movements of the four 7 July suicide bombers as well as the three men who had been charged.
He said it was "highly likely" that more arrests would be made and described the 7 July investigation as a "complicated jigsaw with thousands of pieces".
"We now have enough of the pieces in the right places for us to see the picture, but it is far from complete. Because of that, the search is not over."
The three men are due to appear at London's City of Westminster Magistrates' Court on Saturday.