THE HAGUE (Reuters) -- Prosecutors on Monday formally charged a Congolese militia leader with enlisting children as young as 10 and forcing them to fight in the country's civil war in the first case at the International Criminal Court.

Thomas Lubanga, who was delivered to the court from the Democratic Republic of Congo (DRC) in March, was the founder and leader of one of the most dangerous militia in Congo's lawless northeastern district of Ituri, according to prosecutors.

"Lubanga ... controlled and executed a deliberate plan to enlist and conscript children systematically and in large numbers, including children under the age of 15, even as young as 10," the International Criminal Court's (ICC) deputy prosecutor Fatou Bensouda told a news briefing.

The charges against Lubanga, leader of the Union of Congolese Patriots (UPC), an ethnic militia now registered as a political party, relate to the period between July 2002 and December 2003, although the war in the Congo began in 1998.

The Court will examine the prosecutors' evidence, based on the cases of a representative six child soldiers, in September to decide whether it is sufficient for the trial to go ahead.

Up to 30,000 children were associated with the DRC's armed groups during the height of the war, according to estimates.

"The conscription, enlistment and active use of children in armed conflict represents one of the most brutal and morally troubling legacies of war ..." Bensouda said.

The prosecutors' indictment details how the children, who often joined the militia because of their desperate need for food or desire to avenge their murdered families, were subject to systematic military training and severe discipline.

Commanders urged them to kill members of the Lendu ethnic group in Ituri without instructing them to differentiate between soldiers and civilians, prosecutors said.

Bensouda said the trial would focus on the charges relating to child soldiers but Human Rights Watch (HRW) said in a statement to the court last month such charges did not go far enough, stressing Lubanga's UPC was responsible for much more.

"We believe that you, as the prosecutor, must send a clear signal to the victims in Ituri and the people of the DRC that those who perpetrate crimes such as rape, torture and summary executions will be held to account," HRW said.

The controversial ICC was set up as the first permanent global war crimes court to try individuals and it issued its first warrants last year for five leaders of Uganda's Lord's Resistance Army (LRA).

Ituri has been a bloody corner of Congo where ethnic violence between the Hema and Lendu and clashes between militia groups vying for control of mines and taxation have killed 60,000 people since 1999.