Sudan said South Sudan was supporting a rebel attack on a town in the border state of South Kordofan and building up troops at an oil-producing border area where both countries fought for two days, state news agency SUNA said on Friday.

The neighbouring countries' armies clashed this week at several areas of their poorly marked border, in the worst such violence since South Sudan's secession in July.

The fighting ended when southern troops moved out of the disputed Heglig oil field on the Sudan side of the border after Juba accused Khartoum of bombing southern oil fields.

Sudanese army spokesman Sawarmi Khaled Saad told SUNA that South Sudan's army, or SPLA, was supporting rebels of the SPLM-North with a two-day assault on the border town of Talodi in South Kordofan.

"South Sudan supported the rebels with tanks and artillery," he said, adding that rebels on Friday had attacked the town with artillery but failed to take it. Rebels fled to regroup to launch another attack.

There was no immediate comment from the SPLM-North rebels or the SPLA.

The Sudanese army accused the SPLA of amassing troops at the border south of Heglig. "The goal is to attack the Heglig area another time," Saad said.

Fighters of the Darfur rebel group Justice and Equality Movement (JEM) were joining the troop build-up, he said. Darfur is the scene of an almost decade-long insurgency against the government in Khartoum.

The Heglig field is key to Sudan's economy because it produces around half of the country's oil output of 115,000 barrels a day.

The field was awarded to Sudan by the Permanent Arbitration Court in 2009 but some southern officials have laid claim on it.

The states of South Kordofan and Blue Nile are home to populations which sided with the south during the civil war but were left on the Sudan side of the border. The Sudanese army has been fighting SPLM-North in both states since last year.

Sudan and South Sudan have yet to agree on how much the South should pay to export its oil through Sudan, on how to mark their joint border and on a solution for Abyei, another disputed region.

Both sides are to resume talks in Addis Ababa on Saturday but diplomats see no breakthrough after Sudan's President Omar Hassan al-Bashir called off a summit with his southern counterpart Salva Kiir due to the violence.