The International Criminal Court on Thursday sentenced Dominic Ongwen, a former Ugandan child soldier who became a commander of the Lord's Resistance Army, a rebel group, to 25 years of imprisonment.

The 45-year-old Ongwen was found guilty of 61 crimes comprising crimes against humanity and war crimes, committed in Northern Uganda between July 1, 2002 and December 31, 2005.

He was found guilty of murder, torture, rape, sexual slavery, enslavement and conscripting children under the age of 15 into the Sinia brigade, one of the four brigades of the rebel group, and using them to actively participate in hostilities.

Bertram Schmitt, the presiding ICC judge, said the chamber weighed the mitigation of the circumstances of Ongwen's childhood, his abduction by the Lord's Resistance Army at a very young age and his early stay with the rebel group.

"The chamber was confronted in the present case with a unique situation. It is confronted with a perpetrator who willfully and lucidly brought tremendous suffering upon his victims," Schmitt said.

"However, it is also confronted with a perpetrator who himself had previously endured extreme suffering himself at the hands of the group of which he later became a prominent member and leader."

In its determination of the joint sentence for all the crimes for which Dominic Ongwen was convicted, the chamber declined to sentence him to life imprisonment, considering his individual circumstances and in order to envisage a concrete prospect for him to eventually rebuild his life.

Schmitt said the period of his detention between Jan 4, 2015 and May 6, 2021, will be deducted from the total time of imprisonment imposed on him.

"The sentence may be appealed before the ICC Appeals Chamber by either party to the proceedings," he said.

Born in Choorum village, Amuru district in northern Uganda, Ongwen was abducted by the Lord's Resistance Army on his way to school between the age of 9 and 14.

After the abduction, he underwent initiation ceremonies including torture and being forced to watch violent rituals of people being killed.

He later rose through ranks, becoming a major at the age of 18 and brigadier of the Sinia Brigade by his late 20s.

In 2013, the US government offered a $5 million reward for information leading to his arrest, transfer or conviction.

Ongwen became the first Lord's Resistance Army suspect to be transferred into ICC custody following his January 2015 surrender to US troops in the Central African Republic. His trial opened on Dec 6, 2016.

Since its inception in 1987, the Lord's Resistance Army has committed numerous atrocities against civilians across Uganda, Central African Republic, the Democratic Republic of Congo and South Sudan.

According to the UN Security Council, the rebel group has been involved in elephant poaching and elephant trafficking for revenue generation.

The council said the Lord's Resistance Army reportedly traffics ivory from Garamba National Park in northern DR Congo to Darfur, in Sudan, to trade for weapons and supplies.