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Sudan has declared a state of emergency in areas bordering South Sudan, giving authorities there wide powers of arrest and detention.

A decree carried by the state media on Sunday also included the creation of "special tribunals" to try suspects facing terror and customs offenses.

The move, together with the arrest on Saturday of three foreigners and a South Sudanese in a disputed border area, are signs of spiking tensions along the disputed border, where clashes have raged in recent weeks.

The violence has brought the two nations, already at odds over demarcating the border and dividing oil revenue, to the brink of war.

South Sudan won independence last year as part of a peace deal that ended a long, bloody civil war.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

KHARTOUM, Sudan (AP) — Sudan has claimed three foreigners arrested in a disputed area on the border with South Sudan had military hardware and an armored vehicle. But a representative for one of the three said Sunday that they were on a humanitarian mine-clearing mission.

A Briton, a Norwegian, a South African and a South Sudanese were captured by Sudanese troops Saturday in the oil-rich region of Heglig.

The arrests are the latest sign of spiking tensions along the disputed border, where clashes have raged in recent weeks. The violence has brought the two nations, already at odds over demarcating the border and dividing oil revenue, to the brink of war.

Sudanese army spokesman Col. Sawarmi Khalid Saad claimed on state television late Saturday that the four people arrested had military backgrounds. He alleged they were carrying out military activities in Heglig, but did not elaborate. He said the arrests supported claims by the Sudanese government in Khartoum that South Sudan used "foreigners" when it captured Heglig.

South Sudan seceded from the north last year after a referendum held as part of a 2005 peace deal that ended more than 20 years of civil war between the two sides. But unresolved issues, such as the sharing of oil revenues and demarcation of the border, have led to the new flare-up of violence.

South Sudan invaded Heglig earlier this month, saying it belonged to the south. Sudan later retook the town; Sudanese forces say they pushed out the South Sudanese while South Sudan says its troops pulled out to avoid an all-out war. Sudan elevated the tension even further by bombing South Sudan.

In Oslo, a Norwegian humanitarian organization said Sunday that one of its employees, 50-year-old John Soerboe, was detained while on a five-day mine-clearing mission in southern Sudan with the Briton and South African.

The group denied he was on a military mission and said he had been working for more than seven years to clear the region of mines.

The Norwegian People's Aid organization called Soerboe "one of our most experienced aid workers." Per Nergaard, the group's head of emergency preparedness, said Soerboe used to be in the Norwegian military years ago before turning to humanitarian work. He had been working in southern Sudan since 2005.

He said in a statement on the group's website that Soerboe was on a "routine" mission, with the representatives from South Sudan and U.N. anti-mine organizations, in a region that borders Sudan.

Nergaard did not know the names of the others arrested, or have details about the incident. They were taken by Sudanese authorities to Khartoum, he said.

"The circumstance surrounding their arrest and exact location at the time is yet unclear," he said.

"Our main priority now is to ensure that Soerboe and his colleagues are safe and to assure their rapid release. We are working closely with the Norwegian Foreign Ministry and our U.N. partners to assure this," Nergaard said.

The Norwegian organization has been working in the area since 1986, he added.

A spokesman for the Norwegian Foreign Ministry, Frode O. Andersen, said Oslo "had demanded access to the Norwegian citizen."

"We have asked for a clarification on why he was arrested, and we want to find out the charges against him," Andersen said.

Britain's Foreign Office confirmed a British national had been detained and said it was "urgently investigating" the details of the arrests. The ministry said it had requested immediate access to the Briton, but had no other details.

The South African Foreign Ministry said Sunday it is following up on reports of the arrest of a South African man in a mine clearing detail near the South Sudan border.

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Associated Press writers Jan M. Olsen in Copenhagen, Denmark, David Stringer in London, and Angus Shaw in Harare, Zimbabwe contributed to this report.