The war crimes trial of Lt Col Bedi Mobuli Egangela will be a test case for military justice, the UN mission in the Democratic Republic of Congo says.
Lt Col Egangela is denying charges of war crimes including murder, rape and torture allegedly committed during conflict in the east of the country, in 2005-2006.
"He's a very symbolic case. He has committed many of the most serious crimes that we see all too often in DR Congo," said the UN's Scott Campbell told the BBC.
"The UN Security Council and different special representatives of the [UN] secretary general have been very focused on this case as a bit of a test case to see if military justice can deliver justice for very serious crimes - and committed by a senior officer within the Congolese army," he added.
The trial of Egangela, also known as "Colonel 106", began on Monday in South Kivu and is expected to last for about three weeks, the BBC says.