Mr Lubanga's case would be the first trial at the ICC
Judges at a key war crimes tribunal have reprimanded those prosecuting Congolese warlord Thomas Lubanga and are considering releasing him.
The International Criminal Court (ICC) judges said that evidence had been withheld from the defence.
Mr Lubanga was held in 2006, accused of recruiting and using child soldiers in DR Congo during its brutal five-year civil war, which ended in 2003.
The case would be the first ever to come to trial before the ICC.
The trial had been scheduled to start on 23 June, but judges postponed it following complaints from the defence that prosecutors had not handed over about 200 documents.
The papers included "a significant body of exculpatory evidence", the judges said in their ruling, which was released on Monday.
"The trial process has been ruptured to such a degree that it is now impossible to piece together the constituent elements of a fair trial," the judgement stated.
They will meet on 24 June to decide whether Mr Lubanga should be freed and the case against him halted.
Four million people are estimated to have died during the conflict in the DR Congo.
Mr Lubanga led the Union of Congolese Patriots (UPC) militia in the north-eastern Ituri district, where fighting continued long after the official end of the war.
In a statement released early last year, the prosecution argued that children had been snatched as they walked to school and forced to fight for Mr Lubanga's ethnic Hema militia against their Lendu rivals.
The child soldiers were later instructed "to kill all Lendu including men, women and children", the prosecution statement said, based on testimony from six children.
Mr Lubanga denied any wrongdoing. His lawyers said he was trying to end the conflict and is being punished by the international community for refusing to give mining concessions in areas he controlled to foreign firms.
The ICC, based in The Hague, was set up in 2002 as the world's first permanent war crimes court.
It was designed to end the need for various ad hoc war crimes courts - including the chambers created to deal with war crimes committed in the former Yugoslavia and the genocide in Rwanda.