The army of southern Sudan says gunmen killed 23 people, including policemen and soldiers, in an ambush on a truck in the oil-producing region.
An army spokesman, Malaak Ayuen Ajok, says the attack took place in Unity state on Sunday. He says it was not immediately clear who was responsible. Ajok says the area where attack occurred is usually peaceful.
In a separate incident, Ajok says authorities are still investigating the passengers on an aircraft captured on Sunday while heading to Sudan's capital, Khartoum.
The passengers are accused of supporting renegade southern general George Athor, who began a rebellion in April after losing an election.
Southern Sudanese leaders have accused the north of trying to destabilize the region, which is still recovering from the long north-south civil war.
The semi-autonomous south is scheduled to hold a referendum on full independence next year. The vote is part of the 2005 peace deal that ended the civil war.
Some information for this report was provided by AFP and Reuters.