This was the first sentence the court has handed down since it was set up a decade ago to punish the world's worst criminals.

Lubanga was found guilty in March of abducting boys and girls under the age of 15 and forcing them to fight in a war in the east of the Democratic Republic of Congo in 2002 and 2003. At least 60000 people are thought to have been killed.

"The trial and sentence handed down today send a strong message to those who recruit and use children in war," said Anneke van Woudenberg, of Human Rights Watch.

But Lubanga's sentence has only eight years to run.

The court's critics have questioned how big an achievement it could claim in sentencing Lubanga.

"If you'd said at the beginning [that] this court would finish one trial in 10 years, and that would be for a secondary offence such as using child soldiers, people would have said they won't waste their money on it," said Middlesex University law professor William Schabas.

Some Congolese were disappointed by the sentence.

"We had hoped he would stay in prison for life in order to ease the minds of the victims," said human rights lawyer Emmanuel Folo.

The court's presiding judge, Adrian Fulford, criticised founding prosecutor Luis Moreno Ocampo for his handling of the case.

Some of Moreno Ocampo's detractors said he had focused too strongly on bringing prosecutions against Africans - but his defenders said that that was because Africa's own justice systems were not able to cope.

Lubanga's Union of Congolese Patriots fought against militias of the Lendu ethnic group, including the Congolese Popular Army and the Patriotic Resistance Force, in the Ituri region of the DRC.

Suspects include Laurent Gbagbo, the former president of Ivory Coast, who is in The Hague awaiting confirmation of charges of crimes against humanity in his country.

But other accused remain at large.

They include President Omar Hassan al-Bashir, of Sudan, indicted in 2009 for war crimes in Darfur.

Ugandan warlord Joseph Kony, the subject of a worldwide internet campaign last year, is accused of enslavement and using child soldiers .