Four United Nations deminers arrested by the Sudanese army along the country's tense southern border were released on Sunday and turned over to chief African Union mediator Thabo Mbeki, the defence minister said.

"We release them to President Mbeki," Abdelrahim Mohammed Hussein said in a ceremony at Sudan's military headquarters in Khartoum, more than three weeks after the men were detained.

Mbeki has been in the Sudanese capital since Thursday meeting officials, including President Omar al-Bashir, in an effort to push Sudan and South Sudan back to negotiations which were suspended after border fighting last month.

"I raised your issue with President Bashir and the government explained to us the circumstances of your arrest, and then we asked President Bashir to release you," Mbeki said, addressing the four men, a Briton, a Norwegian, a South African and a South Sudanese.

"All of us will go together," he said before the freed men got into a minibus to leave as part of Mbeki's motorcade.

It was not immediately clear whether they were heading directly to the airport.