South Sudanese rebels on Monday said they had shot down a Ugandan military helicopter fighting on the government side, killing the two pilots and the entire crew.
Rebel spokesman, Dickson Gatluak, said the helicopter was downed early Monday in Kodok, near the northern oil town of Malakal, which has seen an upsurge in fighting in recent weeks.
Meanwhile, Philip Aguer, South Sudanese army spokesman, denied that a helicopter had been shot down, but admitted that Kodok was under rebel control.
Joseph Contreras, a spokesman for the UN mission in South Sudan, said he did not yet have information on the alleged incident.
Uganda has thousands of troops in South Sudan helping President Salva Kiir fight the rebels headed by his long-time political rival and former deputy, Riek Machar.
Rebels have previously claimed to have shot down Ugandan helicopters but the claims have not been confirmed.
South Sudan was an important business partner for neighbouring Uganda but thousands of Ugandans had to be evacuated from the country after the military conflict broke out in December 2013.