SAN JUAN, Puerto Rico - The U.S. military abruptly dropped charges against five Guantanamo Bay detainees, including one who allegedly plotted to detonate a "dirty bomb" in the United States, after a prosecutor charged the military was suppressing evidence that could have helped clear them.

But despite the decision, announced Tuesday, there are no plans to free the men. New trial teams are taking another look at the evidence, the military said, and after consulting with intelligence agencies will recommend whether to reinstate charges.

That means the administration of the next U.S. president will probably get to decide what to do with the cases, including that of Binyam Mohamed, accused of plotting with U.S. citizen Jose Padilla to set off a radioactive bomb and fill apartments with natural gas to blow up buildings.

Padilla was sentenced in Miami to more than 17 years in prison on charges of supporting terrorism after the "dirty bomb" allegations were discarded.

Lawyer Clive Stafford Smith has gone to U.S. and British civilian courts to obtain evidence that Mohamed, an Ethiopian who moved to Britain as a teenager, was tortured and falsely admitted to crimes to halt his agony.

Last month, army Lt.-Col. Darrel Vandeveld, the prosecutor in all five cases, said the military was withholding evidence that could have helped clear the defendants. He resigned in what he called a crisis of conscience.

Stafford Smith said Vandeveld's accusations led to the dropped charges, though the Pentagon denied it. He said the military has already told him it plans to file new charges against Mohamed within a month.

"Far from being a victory for Mr. Mohamed in his long-running struggle for justice, this is more of the same farce that is Guantanamo," Stafford Smith said.

Sixteen of the 255 men at Guantanamo Bay, a U.S. military base in southeast Cuba, now face charges in the first American war-crimes trials since the end of the Second World War. The military had previously dropped charges against a Saudi who allegedly had hoped to become a Sept. 11 hijacker.

In addition to Mohamed, the military dropped charges against Ghassan Abdullah al Sharbi, a U.S.-educated Saudi who allegedly plotted to bomb U.S. troops in Afghanistan; Jabran Said Bin al Qahtani, a Saudi charged with helping al-Qaida make bombs in Pakistan; and Sufyiam Barhoumi of Algeria and Noor Uthman Muhammed of Sudan who allegedly trained al-Qaida recruits in Afghanistan.

The American Civil Liberties Union said the decision to drop the charges "underscores the complete failure of the indefinite detention system and the need to shut down the prison."

"The implosion of these five prosecutions painfully underscores how the Bush administration's torture and detention policies have failed to render justice in any sense of the word," said Anthony Romero, executive director of the ACLU.

But Charles (Cully) Stimson, a former deputy assistant secretary of defence for detainee affairs, said the decision could be an indication that the military court wants to make sure the evidence can be prosecuted beyond a reasonable doubt.

"Generically, it is a healthy sign when the charging authority does not rush to judgment," Stimson said.

The war-crimes trials -- which admit hearsay evidence and testimony obtained under harsh interrogations -- have created many critics, including Vandeveld and three other former Guantanamo prosecutors.

The chief Guantanamo prosecutor, army Col. Lawrence Morris, said the decision to drop the charges was unrelated to Vandeveld's accusations and attributed it to evidence "being more thoroughly analyzed." He would not elaborate on the nature of the evidence but said the review began before Vandeveld criticized the war-crimes trials as a defence witness last month.

But air force Maj. David Frakt, the lead defence lawyer in another case that was being prosecuted by Vandeveld, said the Pentagon's action is "a recognition of the validity of Vandeveld's concerns." He said the Pentagon was also suffering the consequences of rushing cases.

"In the relentless push to bring charges to trial against as many people as possible prior to the election, many detainees were charged before the prosecution was ready," Frakt said.

Army Lt.-Col. Bryan Broyles, who represents al Qahtani, said the military might be preparing the tribunals to face increased scrutiny following the election. John McCain and Barack Obama have both said they want to close Guantanamo Bay.

The military also said Tuesday it has finalized charges against an additional detainee, Mohammed Hashim, an Afghan who is about 32. He is accused of providing material support to terrorism and spying, and could face life in prison.