The SPLM won a landslide across Southern Sudan
At least eight people have been killed when mutinous troops attacked an army base in south Sudan following this month's elections, officials say.
A southern army spokesman said the mutineers backed a former general who ran and lost in a Jonglei state poll.
George Athor denied leading the troops but told the BBC he sympathised with them and said the polls were rigged.
The ex-rebel SPLM party won a landslide victory to retain power in the south, amid widespread claims of intimidation.
The 11-15 April elections were the first in 24 years - and the first since the end of a two-decade conflict between north and south.
The BBC's James Copnall in Khartoum says there have been intense negotiations for several days to avoid just this sort of problem in Southern Sudan.
Several senior southern soldiers contested the elections as independents and all but one lost.
Mr Athor ran for governor of Jonglei state as an independent when he did not get the SPLM nomination.
The Delab Hill barracks, 12km (7 miles) south of Malakal, were attacked.
The army spokesman said weapons were stolen.
"We managed to push back the attackers, but there are seven dead and nine injured among the troops," southern army spokesman Malaak Ayuen Ajok told AFP.
"Several attackers also lost their lives."
Malakal was the scene of fierce fighting between rival militias in 2009, and in 2006, which left at least 150 people dead.
Our correspondent says it is too early to tell if this is an isolated incident, or the start of a much bigger problem.
He says the voting process itself was largely peaceful, but tensions rose, particularly in the south, as accusations of electoral fraud began to multiply.
SPLM leader Salvia Kiir won 93% of the vote in the southern presidential election.
A referendum is due in January 2011 in the semi-autonomous south on whether the region should secede from the mainly Muslim and Arab-dominated north.