WASHINGTON - The US government has withdrawn key allegations linking a British prisoner held at Guantanamo Bay, Cuba, to a plot to detonate a radioactive dirty bomb. Defence lawyers said the decision should force federal officials to drop charges of conspiracy and material support for terrorism against Binyam Muhammad, The Washington Post reported. Binyam's attorneys said the charges filed in May were based on false confessions obtained through torture. The govt alleged Binyam, 30, was involved in a plot to explode a radioactive dirty bomb in US locations, blowing up apartment buildings and releasing cyanide gas in nightclubs. "There are no serious, hard charges against Binyam," said Air Force Lt-Col Yvonne Bradley, the British prisoner's  attorney. "The whole thing the government was hanging its hat on, pursuing Binyam, was the dirty bomb." Binyam's case is "under review", Joseph DellaVedova, a spokesman for the Office of Military Commissions, told the Post. The Justice Department's decision came after a Washington federal judge ordered the government to turn over all available exculpatory evidence to Binyam's attorneys, documents filed by government attorneys indicated. The order covered classified British intelligence documents that included communications with US officials about Binyam Muhammad after his arrest in Pakistan in April 2002.