JUBA, Sudan (Reuters) - At least two people were killed during a clash between security forces and supporters of an independent candidate in elections in south Sudan's oil-producing Unity state on Friday, the United Nations said.

The deaths were the first serious violence reported during the announcement of results in Sudan's complex presidential, legislative and gubernatorial ballots.

Sudan is in the closing stages of its first open polls in 24 years, a process already marred by delays, boycotts and opposition accusations of widespread vote rigging.

The elections, set up under a 2005 peace deal that ended more than two decades of north-south civil war, were designed to help transform Africa's largest nation into a democracy.

The violence erupted in the state capital Bentiu after a radio announcement said Angelina Teny had lost the race to become Unity governor to incumbent Taban Deng Gai, a member of Teny's campaign team told Reuters, asking not to be named.

"From what I understand there was some sort of a demonstration over a gubernatorial radio announcement," U.N. regional coordinator for southern Sudan David Gressly told Reuters.

"It's not clear how it happened but there seems to have been some shooting and two people were killed and four were wounded."

Gressly said it appeared security forces had tried to disperse the crowd. The dead and injured were all civilians, he added.

Teny, the wife of South Sudan's Vice President Riek Machar, told Reuters she had reports one of the injured people died later from their wounds.

Sudan's National Elections Commission (NEC) announced late on Friday that Gai, from the south's dominant Sudan People's Liberation Movement (SPLM), won the gubernatorial race with 137,636 votes, with Teny in second place with 63,500 votes.

Teny said that she would contest the outcome. During the election period she complained her agents had been harassed and arrested.

Teny was running as an independent after failing to get the SPLM nomination.

Southern officials told Reuters they were tightening security in two other southern states where independents ran against SPLM candidates.

Earlier on Friday, SPLM secretary general Pagan Amum told reporters the party won overwhelming victories at all levels of elections in the south.

The 2005 accord set up a semi-autonomous southern government and promised a referendum on southern secession in 2011.

Early results suggest Sudan's incumbent president Omar Hassan al-Bashir will keep the top job while his northern National Congress Party will retain control of the national assembly.