Sudan has declared a state of emergency along the border with South Sudan, giving Khartoum broader powers to arrest and try suspects in the volatile region.
Khartoum's official news agency SUNA reports Sunday the decree allows President Omar al-Bashir and "anyone with his mandate" to set up "special courts" to handle criminal and terror cases.
The measure also suspends the constitution in border areas and imposes a trade embargo against South Sudan.
The action signals a continued push toward all-our war as hostilities between the neighboring countries intensify over oil revenue, border demarcation and citizenship disputes.
Also Sunday, an aid group says foreigners arrested by Sudan in the contested Heglig area were de-mining the border area, contrary to claims by Khartoum they were spying for the south.
Sudan arrested a Briton, a Norwegian, a South African and a South Sudanese in the oil-producing area on Saturday.
Pro-Sudanese media (Sudanese Media Center) quote defense officials saying the suspects were collecting "war-related" items and holding "military" material.
An official with the Norwegian People's Aid (NPA) 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.
The international community has called on both sides to end hostilities and resume peaceful dialogue.
Some information for this report was provided by AP, AFP and Reuters.