Sudan has released four foreigners who were detained last month in the disputed Heglig region and accused of spying for South Sudan.

The defense ministry handed the four on Sunday to former South African president and African Union mediator Thabo Mbeki.

The four appeared to be in good health during a ceremony in Khartoum, which took place one day after Mr. Mbeki met with President Omar al-Bashir.

The mediator is working to convince the two Sudans to resume negotiations that came to a halt last month, after clashes broke out between the two sides in the Heglig area.

Sudanese soldiers accused the foreigners of illegally entering Heglig to spy for the south.

Aids groups said the four – a Briton, a Norwegian, a South African and a South Sudanese – were in the oil-rich region to remove mines.

After being released, Norwegian John Sorbo thanked the Sudanese government on behalf of the group.

Sudan has accused South Sudan of using foreigners to help capture the oil-producing Heglig region in early April. Days later, northern forces recaptured Heglig.

The two countries had been in negotiations to resolve disputes over border demarcation, oil revenues and citizenship questions.

The United Nations has called on both sides to bridge their differences through peaceful negotiations.

The two countries formally split in July, when South Sudan declared independence from the north.