"Several attackers also lost their lives."
The army said it had captured some of the attackers who said they were acting under the orders of George Athor Deng, an SPLA member who ran as an independent for governor in the southern Jonglei state but was defeated by Kuol Manyang.
"He's very angry to have lost. We have no other explanation for this attack right now," Ajok said.
Deng was not immediately available for comment.
Khartoum, which signed a peace agreement with the SPLM/SPLA in 2005 ending a decades-long civil war, held multi-party presidential, legislative and local elections between April 11-15, the country's first since 1986.
The election was part of the peace deal under which the SPLM runs a semi-autonomous government and an army, and will be followed by a referendum on the indepepende of southern Sudan in January 2011.
Omar al-Bashir, the Sudanese president wanted by the International Criminal Court over war crimes in the Darfur in region, worn re-election after several major parties boycotted the poll, citing irregularities.
Last week, two people were killed in the southern unity state when police opened fire on supporters of independent candidate Angeline Teny who was running for governor but was defeated by Taban Deng, the incumbent.
In another development, the president of southern Sudan has expressed concern over military movements by northern forces, according to Suna, Sudan's official news agency.
The agency said on Saturday that a letter from Salva Kiir, the southern president, had been delivered to al-Bashir detailing northern military movements in and near the south.
Kiir's letter documented Sudanese movements including in the states of South Darfur and Blue Nile, which is on the northern side of the border but near a spot in the south where Sudanese troops reportedly clashed with southern rebels.
Darfur rebel group the Justice and Equality Movement (Jem) accused Sudanese troops on Friday of launching a major attack on its positions despite a framework peace pact signed in Qatar in February.