A United Nations official says that South Sudan's rebels are holding 13 U.N. contractors in Upper Nile state.
The U.N. is engaging with the rebels to release the men, U.N. information officer Shantal Persaud told The Associated Press on Sunday.
The U.N. earlier said 12 local contractors were detained after the rebels released 18 international peacekeepers Thursday. The rebels captured the men last week when they seized a U.N. barge carrying fuel along the Nile River. Rebels control the river's west bank. The U.N. has bases on the government-controlled east side of the river.
The rebels said they took the vessel because they thought it was delivering weapons to government troops and carried army soldiers and members of the domestic spy agency. South Sudanese nationals working for U.N. agencies have been kidnapped and killed in the past along the Nile.
Government army spokesman Col Philip Aguer denied that any government soldiers were on board, and accused the U.N. of assisting the rebels. Rebels have previously used barges to carry forces and ammunition, he said.
The U.N. denied the barge carried weapons cargo and said the fuel was meant for use by the U.N., not by the opposition, according to a statement by Ellen Loj, head of the U.N. mission in South Sudan.
South Sudan has been at war since 2013 between President Salva Kiir's forces and rebel leader Riek Machar. Although the warring factions signed a peace deal in August, fighting persists, especially the contested states of Upper Nile and Unity.