Sudan says three foreigners and a South Sudanese arrested in the disputed Heglig region were apparently spying, but an aid group say the detainees were de-mining the area.

Khartoum arrested a Briton, a Norwegian, and a South African on Saturday, in the latest flare-up along Sudan and South Sudan's volatile border.

Sudanese officials claim the three entered into the contested area without proper visas and were conducting spying activities for the south.

Pro-Sudanese media quote defense officials saying the suspects were collecting “war-related” items and holding “military” material.

An official with the Norwegian People's Aid mission said one of its employees was arrested with a team contracted to de-mine the area.

The British and Norwegian embassies said Sunday they are investigating the circumstances surrounding the arrests.

The detainees have been flown to Khartoum for questioning.

Sudan has accused South Sudan of using foreigners to help capture the oil-producing Heglig region earlier this month.

Last week, the north said it has recaptured Heglig.

Fighting between the two countries has increase in the last year, prompting fears the two Sudans are on the brink of a full-blown war.

The international community has called on both side to end hostilities and return to peaceful talks to resolve bitter disputes over border demarcation, oil revenues and citizenship questions.