WikiLeaks has more classified information Bradley Manning leaves court after a motion hearing in Fort Meade, Maryland. Julian Assange has confirmed that WikiLeaks still holds classified United States government documents that it is yet to publish. However the transparency website will not release this material during the court martial of its source, US Army private Bradley Manning. Speaking to Fairfax Media, Mr Assange said on Tuesday that Manning was "America's foremost political prisoner ... an activist who faces retribution for revealing the truth." Julian Assange at the Ecuadorian embassy in London. Manning last Thursday publicly accepted responsibility for providing WikiLeaks with hundreds of thousands of secret US military and diplomatic reports, telling a US military court that he did so to spark public debate on US foreign policy and military operations in Afghanistan and Iraq. "Bradley Manning's plea was a very positive development for him," Mr Assange said. For the first time he was able to speak about his motivation to reveal truths and stimulate public debate about war. The US Government has repeatedly sought to deny or suppress Manning's motivation for his actions, and the tabloid press has tried to strip him of any political motivation. Manning's leaks of classified information to WikiLeaks took place between February and April 2010. He has pleaded guilty to a range of charges that carry a maximum penalty of 20 years' imprisonment. Despite Manning's guilty plea, US military prosecutors have confirmed their intention to pursue Manning on other more serious charges, including that of "aiding the enemy," which carries a potential life sentence. Manning's civilian lawyer, David Coombs, has indicated Manning will "vigorously contest" these charges at his trial, which is scheduled to begin on June 3. Mr Assange yesterday confirmed to Fairfax Media that WikiLeaks had received classified material from Manning that related to a February 2010 incident in which the US military had turned a blind eye to Baghdad police arrests and persecution of political opponents of Iraqi Prime Minister Nouri al-Maliki. In his statement last Thursday, Manning said that in early March 2010 he had been disappointed when his anonymous contact at WikiLeaks told him they "needed more information to confirm the event in order for it to be published or to gain interest in the international media." Mr Assange said yesterday that WikiLeaks had decided not to publish the material at the time for "source-protection reasons" given that the person providing the material appeared to have been connected with the US military's handling of the incident. Mr Assange said that notwithstanding Manning's courtroom admission of responsibility for the disclosure, protection of the source remained a consideration. We still can't publish it. It would be a questionable action to do so now while Bradley Manning has a potential life sentence hanging over his head," he said. Mr Assange declined to elaborate on Manning's admission that he also sent what he publicly described as "other government documents" to WikiLeaks. Manning, who had access to top-secret US intelligence databases, said that in March 2010 he "read several documents from a section within (a) government entity. The content of two of these documents upset me greatly. I had difficulty believing what this section was doing. He said he subsequently uploaded the two documents to WikiLeaks confidential electronic drop box. It is alleged by prosecutors that Manning passed to WikiLeaks "more than one classified memorandum produced by a United States government intelligence agency." On March 26, 2010, WikiLeaks published a Central Intelligence Agency "Red Cell" memo, dated March 11, on public relations strategies to sustain Western European support for the NATO military campaign in Afghanistan. Subsequently, on August 25, 2010, WikiLeaks also released a second CIA memorandum, dated February 5, 2010, on foreign perceptions of "home-grown terrorism" in the United States. Mr Assange yesterday said he "wouldn't go beyond what Manning has said" and "can't answer" whether the two published CIA documents were the documents referred to by Manning or whether WikiLeaks holds other intelligence agency material not yet published. "I can't say anything that might suggest that someone had been responsible for, or was party to, any further disclosure," he said. Mr Assange did confirm that WikiLeaks received videos and other documents relating to a May 2009 US air strike near Granai village in Afghanistan that killed between 90 to 150 Afghan civilians, including many children. Manning, who admitted he sent the material to WikiLeaks in late March 2010, said the Granai attack involved "a significantly higher number of individuals, larger aircraft and much heavier munitions" than the July 2007 helicopter gunship attacks in Baghdad which were the subject of another video he passed to WikiLeaks and which the transparency group released in April 2010 under the headline "Collateral Murder." Mr Assange said the Granai air strike material "documented a massacre, a war crime." He disputed previous media reports claiming WikiLeaks had been unable to open the encrypted video files. WikiLeaks obtained this material and scheduled it for release, but the opportunity to reveal these important records was lost when Daniel Domscheit Berg left WikiLeaks, taking this and other material with him, which he has said he later destroyed. "WikiLeaks no longer has a copy," Mr Assange said. A US military inquiry into the Granai air strike found that US air crews and troops on the ground did not follow rules of engagement devised to prevent civilian casualties. Videos of the air strikes have not been published.