By Michelle Nichols
UNITED NATIONS (Reuters) - Eighteen United Nations peacekeepers in South Sudan were freed on Thursday after being held for three days by heavily armed rebels, but a dozen U.N. contractors who were operating a fuel barge have not yet been released, the world body said.
U.N. peacekeeping chief Herve Ladsous spoke to opposition leader Riek Machar about the incident on Thursday. The United Nations also said it is "extremely concerned" about the South Sudanese crew of the fuel barge who were still being held.
U.N. spokesman Stephane Dujarric warned that "attacks against peacekeepers and other U.N. staff can constitute war crimes." He called for the return of the U.N. contractors as well as the barge and the weapons that were taken from the peacekeepers.
He said more than 100 rebels seized the barge on Monday north of Malakal, the capital of the oil-rich Upper Nile State, and looted the fuel it was carrying.
A political row between South Sudan's President Salva Kiir and his former deputy Machar sparked civil war in late 2013 and reopened ethnic fault lines between Kiir's Dinka and Machar's Nuer people. More than 10,000 people have been killed.
Kiir and Machar signed a peace deal in August, but since then both sides have accused one another of attacks, and humanitarian groups have pulled out of parts of the oil-rich country where heavy violence has been reported.
Some 13,000 U.N. peacekeepers are still sheltering more than 100,000 South Sudanese at camps throughout the landlocked country. Peacekeepers have been deployed in South Sudan since it declared independence from Sudan in 2011.