President Joseph Kabila has said ex-rebel leader Bosco Ntaganda, wanted by the International Criminal Court (ICC) for war crimes, must be arrested.
But Gen Ntaganda must be tried in the Democratic Republic of Congo, the president says. Mr Kabila had previously refused to call for the arrest of the man known locally as "The Terminator".
The ICC indicted him five years ago, for allegedly recruiting child soldiers during DR Congo's bloody five-year war.
'Judged in Goma'
President Kabila held emergency meetings with top army officials in the east of the country, following the defections earlier this month of hundreds of Congolese troops.
The soldiers, loyal to Gen Ntaganda, were integrated into the national army in 2009. However, people in and around the town of Goma, where the troops are based, blame them for persistent unrest – including looting and rape – since the formal end of the war in 2003.
"I want to arrest Bosco Ntaganda because the whole population wants peace," Reuters news agency reports Mr Kabila as saying.
"He has committed crimes in North Kivu and Goma… He will be judged in Goma," he said. Last month the chief prosecutor at the ICC called for Mr Ntaganda's immediate arrest, after the court convicted another former Congolese rebel leader, Thomas Lubanga, of similar offences.
The ICC says Gen Ntaganda used child soldiers for fighting in Ituri, in north-eastern Congo, from 2002 to 2003. He is also wanted for murder and rape. The former rebel's exact whereabouts remains unclear. He is reported to have left the Goma area, taking with him heavily armed soldiers. Some reports put the number of defectors as high as 600. They are reported to have taken vehicles, weapons and ammunition. BBC Africa analyst Martin Plaut says the implication of the defections is clear: if attempts are made to arrest Gen Ntaganda, there will be trouble.
A Congolese army spokesman said that any act of indiscipline would be punished.