A former child soldier accused of being a senior commander in the Lord’s Resistance Army has pleaded not guilty to war crimes in the first trial of its kind at the International Criminal Court.

Dominic Ongwen has been charged with 70 counts including murder, rape, the use of child soldiers and sexual enslavement, relating to the group’s decades-long insurgency in northern Uganda.

Mr Ongwen was himself a child soldier, chief prosecutor Fatou Bensouda told the judges, captured and forced to fight for the warlord Joseph Kony in the late 1980s when he was just 14 years old.

But that was no more than a mitigating factor in his alleged crimes, Ms Bensouda said, as he rose through the ranks on account of his reputation as a ruthless killer.

Judges at The Hague rejected an effort by Mr Ongwen’s lawyers on the eve of his trial to call for psychological tests, saying he may not be mentally fit to plead.

And he seemed disorientated by his surroundings at the global court, requiring repeated prompting to stand and enter his plea.

After an official read out all 70 charges relating to war crimes and crimes against humanity, Mr Ongwen said: “In the name of God, I deny all these charges.

Speaking in his native Acholi through an interpreter, he said: “It was the Lord’s Resistance Army (LRA) who abducted and killed people in northern Uganda, and I am one of the people against whom the LRA committed atrocities.”

Mr Ongwen is the only member of the LRA in the court’s custody, and rights groups welcomed the landmark trial as a long-overdue chance to deliver justice to the insurgency’s victims.

Dominic Ongwen sits in the courtroom of the International Court in The Hague (EPA)

Mr Ongwen becomes the first member of Uganda's brutal Lord's Resistance Army to go on trial (Getty)

He was indicted back in 2005, along with three other alleged senior commanders who are since believed to have died, and Kony himself, who remains at large as the LRA continues to rampage across the Democratic Republic of Congo, South Sudan and the Central African Republic.

Over the course of the trial, which will hear statements this week before pausing to resume next year, the court is expected to hear from other former child soldiers of the LRA and women who were forced into sexual slavery.

Ms Bensouda summed up some of the most horrific evidence against Mr Ongwen, including one former child soldier who will testify that he “ordered this boy and others to kill an old man by biting him and then stoning him to death”.

Describing harrowing acts of sexual violence, Ms Bensouda said Mr Ongwen had raped one child victim vaginally and anally.

"To quiet her when she wept and screamed he threatened her with his bayonet," she told the court, citing the witness's statement.

And Ms Bensouda said the witnesses next year may include a girl who told investigators about Mr Ongwen's repeated rape of sex slaves.

"Dominic was the worst when it came to young girls," Ms Bensouda said, citing the witness. "He has sex with them at a very young age.”

Mr Ongwen gave himself up last year after a decade on the run, and prosecutors specifically accuse him of commanding brutal assaults on four camps for internally displaced people in northern Uganda from October 2003 to June 2004.