A US military judge ruled Thursday that WikiLeaks suspect Bradley Manning can be tried for "aiding the enemy" over allegedly leaking documents to the site -- a charge that carries a potential life sentence.

The decision was another setback for Manning, whose attorneys had argued for the espionage charge to be tossed out unless the government was prepared to prove the US Army private had intended to help Al-Qaeda when he allegedly passed files to WikiLeaks.

The 24-year-old could be jailed for life if convicted of "aiding the enemy," one of 22 criminal charges that judge Colonel Denise Lind let stand at pre-trial hearings this week at Fort Meade in Maryland.

Lind said she would issue instructions on the espionage count to make clear what prosecutors will have to prove against Manning when his trial starts on September 21.

The government will have to show that Manning "knowingly" and without permission passed classified information to the enemy "through indirect means," she said.

Defense lawyers insisted the government's case implies any soldier could be prosecuted for espionage if they inadvertently divulged secrets online or discussed sensitive information with news reporters.

Prosecutors, however, maintained Manning's intent was not at issue and that the government only needed to prove that the intelligence analyst knew Al-Qaeda would see the leaked information on the anti-secrecy WikiLeaks site.

The hearing underlined the legal dilemmas of a digital era as rights groups voiced alarm at the prosecution's tough line over online leaks.

"The implications of the government's argument are breathtaking," said Ben Wizner of the American Civil Liberties Union.

"In its zeal to throw the book at Manning, the government has so overreached that its 'success' would turn thousands of loyal soldiers into criminals," Wizner wrote on ACLU's website.

Manning is accused of leaking hundreds of thousands of military logs from Iraq and Afghanistan and US diplomatic cables to WikiLeaks between November 2009 and May 2010, when he served as a low-ranking intelligence analyst in Iraq.

The judge earlier on Thursday rejected defense motions asking for some of the other counts to be tossed out or combined, after Manning's lawyers alleged the prosecution had "over-charged" their client.

Given the "volume of records" leaked, the counts were reasonable and prosecutors had not "piled on the charges" as the defense argued, the judge said.

The baby-faced Manning, who appeared in court clad in a blue Army dress uniform, has yet to enter a plea in the case.

Lawyers also sparred Thursday over whether the effect of the massive leak was pertinent to the case.

The charges do "not require the United States to prove actual harm" was done but only that secrets were revealed, said prosecutor Major Ashden Fein, who argued for a motion to exclude any discussion of the leak's impact.

Manning was transferred a year ago from a military prison at Quantico, Virginia -- where he had been imprisoned since July 2010 -- to another in Fort Leavenworth, Kansas.

During Manning's eight months of solitary confinement at Quantico, he was subjected to "cruel, inhumane and degrading treatment," according to a UN special rapporteur.

Manning, who has spent more than 700 days in detention, is painted as a traitor by some for his alleged role in the worst ever breach of US intelligence, which embarrassed Washington and dismayed US allies.

But his supporters, some of whom sat in the courtroom watching the proceedings wearing T-shirts inscribed with the word "Truth," view Manning as a political prisoner and praise WikiLeaks for uncovering government secrets.