Media playback is unsupported on your device Media caption Bradley Manning has denied that his leaks helped terror groups such as al-Qaeda

A military judge has refused to dismiss the most serious charge facing Bradley Manning, the US soldier who allegedly leaked thousands of secret documents.

Lawyers for the 25-year-old argued there is no proof he "aided the enemy", a charge carrying a life prison term.

Prosecutors have argued he "systematically harvested" documents eventually seen by Osama Bin Laden.

The case, allegedly involving 700,000 files, is considered the largest-ever leak of secret US government documents.

"He [Pte Manning] was knowingly providing intelligence to the enemy," said Judge Colonel Denise Lind at Thursday's hearing in Fort Meade, Maryland.

The decision does not exclude the possibility of Pte Manning being ultimately acquitted of the charge.

No 'evil intent'

The accused, who appeared to be following the proceedings closely, showed no reaction to the ruling.

He has previously pleaded guilty to 10 of the more than 20 charges he faces.

At the scene Today's ruling from the judge on the charge of "aiding the enemy" was highly anticipated. Outside the court at Fort Meade, Pte Manning's supporters said the case could deter other "whistleblowers" from sharing classified information which might be in the public interest. One of them asked whether, if someone leaked something to a newspaper, they too could be seen as "aiding the enemy". If found guilty on this count, Pte Manning faces life in prison. For him to be convicted, it needs to be proved that he gave potentially damaging information to an enemy, knowingly, and with evil intent. It is this last clause that could be the trickiest to ascertain. Prosecutors argue they have proof al-Qaeda accessed information from Wikileaks, and that by posting the information Pte Manning would have known terror groups could see it.

But on Thursday, Judge Lind also denied a defence request to drop a computer fraud charge.

She is still considering a motion by Pte Manning's lawyers to dismiss five charges of theft.

Some two dozen of his supporters sat quietly in the courtroom, some wearing t-shirts printed with the word "truth".

"We're disappointed," Jeff Paterson, head of the Bradley Manning Support Network, told the Associated Press news agency outside court.

On Monday, defence lawyer David Coombs argued that the Army private was guilty of negligence, but not the "general evil intent" required to justify the life charge.

He said the government had offered no evidence to show that Pte Manning knew the leaked files could fall into the hands of al-Qaeda militants.

Pte Manning's lawyer has sought to show that he was "young, naive and good-intentioned" when he arrived in Iraq, but became disillusioned.

The accused told a pre-trial hearing in February that he had divulged the documents to spark a public debate about US military and foreign policy.

Prosecutors have argued the leaks damaged national security and endangered American lives, and said Pte Manning used his military training and access to gain notoriety.

Among the items sent to Wikileaks was graphic footage of an Apache helicopter attack in 2007 that killed a dozen people in the Iraqi capital Baghdad, including a Reuters photographer.

Other files leaked included thousands of battlefield reports from Afghanistan and Iraq, as well as secure messages between US embassies and the state department in Washington.