A military judge has pushed back the trial of Bradley Manning, the US soldier accused of being behind the WikiLeaks publication of state secrets.

Colonel Denise Lind, the judge presiding over Manning's court martial, has rescheduled the trial for June to allow extra time to deal with classified information. Manning had been due to be tried in March.

The private faces 22 charges, including "aiding the enemy" – which carries a possible maximum sentence of life in military custody without any chance of parole.

On Tuesday Lind had awarded Manning a 112-day reduction in any eventual sentence, on the grounds that he was subjected to excessively harsh treatment in military detention.

The judge granted the reduction as a form of recompense for the unduly long period in which he was held on suicide watch, and prevention of injury status while at the brig at Quantico marine base in Virginia. Manning was detained there from 29 July 2010 to 20 April 2011.

Manning has offered to plead guilty to some of the lesser charges in exchange for a reduced sentence. The most serious accusation levied against the soldier is that by passing information to WikiLeaks, he effectively made it available to al-Qaida and its affiliate terrorist organisations – the "aiding the enemy" charge which carries the punitive life sentence.

Manning was held under constant surveillance while at Quantico. He had his possessions removed from his cell and at times even his clothes, often in contravention to the professional medical opinion of psychiatrists.

Lind's ruling that Manning should receive a reduction in sentence was made under Article 13 of the Uniform Code of Military Justice, which protects prisoners awaiting trial from punishment on grounds that they are innocent until proven guilty.

The recognition that some degree of pre-trial punishment did occur during the nine months that the soldier was held in Quantico marks a legal victory for the defence in that it supports Manning's long-held complaint that he was singled out by the US government for excessively harsh treatment.

However, the ruling falls far short of the hopes of Manning's defence team. At best, the soldier's lawyers had pressed for a dismissal of all 22 counts that he is currently facing relating to the transfer of hundreds of thousands of US diplomatic cables and war logs to the whistleblowing website WikiLeaks.

Dismissal of all charges is listed as a possible remedy for an Article 13 violation. But Lind said it should be used only under the most egregious circumstances where the US government has engaged in outrageous conduct.

"The charges are serious in this case and there was no intent to punish. There is no argument to dismiss the charges," the judge said.

• This article was amended on 10 January 2013. The original sub-heading referred to Bradley Manning as a former US soldier. This has been corrected.