British prosecutors charged three men Thursday for allegedly conspiring in the suicide attacks in London on July 7, 2005 and authorities said they were searching for more suspects.
For the first time, police alleged that the conspiracy also may have involved tourist sites.
All of those charged Thursday were from the same area of West Yorkshire, England, as the four bombers. The attacks killed 52 London subway and bus commuters and wounded over 700.
"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 finalized," prosecutor Susan Hemming said.
The suspects are Mohammed Shakil, 30, of Beeston, a suburb of Leeds; Sadeer Saleem, 26, of Beeston; and Waheed Ali, 23, who recently lived in London but is formerly from Beeston.
They were charged with conspiring between November 1, 2004 and June 29, 2005 to cause explosions on London's transport network "and/or tourist attractions in London of a nature likely to endanger life or cause serious injury."
The three men were due for an initial court appearance Saturday.
Police anti-terror chief Peter Clarke said he expected there would be more arrests in the case.
"The detail of the evidence must wait but it is probably fair to describe it as a complicated jigsaw with thousands of pieces," said Clarke, who read a statement to reporters but took no questions.
"We now have enough of the pieces in the right place for us to see the picture but it is far from complete. Because of that, the search is not over.
"I firmly believe that there are other people who have knowledge of what lay behind the attacks 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. For that reason the investigation continues."