The suspension of the trial of Thomas Lubanga, alleged to have been one of the most dangerous warlords in Africa, has been upheld by the International Criminal Court (ICC).

But Lubanga, who is accused of using child soldiers in his private army during the war in the Democratic Republic of Congo, is to stay in custody after the court refused to order his release on Tuesday.

The judges agreed with a lower court decision that Lubanga was not receiving a fair trial because the prosecutor had effectively prevented the chamber from assessing evidence obtained under confidentiality agreements from the UN.

However, it also accepted the prosecution's appeal against a move to release the defendant immediately returning the decision to the trial chamber.

"The trial chamber is directed to decide anew whether [Lubanga] should remain in detention or whether he should be released with or without conditions," Sang-hyun Song, the presiding judge, said.

'Disappointing development'

"This is a disappointing development for victims," said Christian Hemedi, the co-ordinator of the Congolese National Coalition for the ICC, a group that support's the court's work.

"We were waiting for the proceedings to resume and restore our confidence in the court's first trial," he said.

The UN and other non-governmental groups had provided evidence to investigators on condition that not even judges would be allowed to see it.

But under the rules of the court, prosecutors are obliged to gather evidence that could clear suspects as well as evidence tying them to crimes and it would be possible that some of the secret evidence could have helped Lubanga.

Last week, prosecutors said that the UN had now agreed to give judges "unfettered access" to the documents, a move that could clear the way for Lubanga's trial to start.

Lubanga, who was handed over to the court in 2006, has denied the charges in the case, which would be the first ever to come to trial before the ICC.