FORT MEADE, Maryland (AFP) - A US military judge ruled on Tuesday that delays in the trial of WikiLeaks suspect Bradley Manning were "reasonable" and did not justify throwing out the serious charges against him.

"The motion to dismiss the charges is denied," Judge Denise Lind said at a pre-trial hearing at Fort Meade, Maryland, north of Washington.

Manning's defence lawyers had argued that his right under the military legal code to a speedy trial within 120 days had been violated and appealed to the court to throw out the case, in which he is accused of passing a trove of secret documents to Julian Assange's anti-secrecy WikiLeaks website.

Manning, 25, a former military intelligence analyst in Iraq, has spent more than a thousand days in detention since his arrest in May 2010. He was not formally charged until Feb 23, 2012.

Defence attorney David Coombs had argued the military made an "absolute mockery" of his client's right to a speedy trial and that the proceedings have moved at "a snail's pace."

But the judge disagreed, saying the prosecution's requests for delays were legally valid and necessary, given that the discovery process had required searching for about 380,000 pages of documents.

"The government worked diligently" to retrieve the documents and was justified in requesting seven separate delays of 30-days each, Judge Lind said.

"During each 30 days period, there was progress," she said.

Manning faces a slew of charges, including "aiding the enemy," for allegedly leaking hundreds of thousands of sensitive US military and diplomatic documents to WikiLeaks.

The case involves the largest leak of classified documents in American history.

The defence has argued the case against Manning is virtually unprecedented as US authorities usually prosecute soldiers or government employees who pass secrets directly to an adversary - and not those who leak information to a media outlet or website.