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

Khartoum's defense ministry said it handed the four on Sunday to former South African president and African Union mediator Thabo Mbeki.

Mr. Mbeki is in the region to mediate talks between the two Sudans, who remain locked in bitter disputes more than ten months after the south formally split from the north.

The foreigners include a Briton, a Norwegian, a South African and a South Sudanese. They were detained by Sudanese soldiers in April, sparking protests by aid groups who said the four were in the volatile area to help remove land mines.

Sudan claimed the four entered the contested area without proper visas and were conducting spying activities for the south.

Sudanese authorities did not immediately reveal why they released the foreigners on Sunday.

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 countries remain at odds over border demarcation, oil revenues and citizenship question.

The international community has urged both sides to bridge their differences through peaceful negotiations.