Paradorn led a nine-member delegation to Thursday's talks.
The Thai government and military have struggled to identify legitimate participants for the peace process, as the militant leadership is not clear and no groups have stepped out to take responsibility for the attacks. The insurgency is believed to be highly decentralized, with local units having the freedom to choose targets and campaigns.
The BRN is one of several separatist movements that have made public calls for a separate state in Thailand's south.
"I insist that the BRN movement is unified but it will take some time for them to relay the message to members in the area," Paradorn said.
Just hours before the talks started, suspected militants killed three soldiers in a roadside attack in Narathiwat province.
Police Col. Suchart Sa-eed said militants detonated an improvised bomb and opened fire at soldiers who were on foot patrol in Cho Airong district. He said five soldiers were wounded in the ambush, which took place in a village that is home to a key BRN leader.
The next round of talks is scheduled for April 29.