KHARTOUM, Sudan - Sudan declared a state of emergency Sunday in areas bordering South Sudan, giving authorities wide powers of arrest a day after they detained three foreigners in a flashpoint town along the frontier.

The detentions and state of emergency heightened tensions even further along border between the old rivals, who in the last month came to the brink of an all-out war because of renewed fighting in disputed areas.

Sudanese officials have accused South Sudan of using foreign fighters during its assault on the oil-rich Heglig region, which Sudan claims. Southern Sudanese troops briefly captured the area, amid rising international concerns of an escalation in the fighting between the two countries.

A Sudanese army spokesman, Col. Sawarmy Khaled, claimed on state television late Saturday that four people arrested in the Heglig region, including a Briton, a Norwegian, a South African, and a South Sudanese, had military backgrounds. He alleged they were carrying out military activities in Heglig, but did not elaborate. Khaled said the arrests prove its government claims that South Sudan uses foreign fighters.

But a representative for one of the three said Sunday that they were on a humanitarian mine-clearing mission.

South Sudan split from Sudan in July, but the two countries have yet to agree on border demarcation and divvying up oil revenues and resources.

South Sudan invaded this month, saying Heglig belonged to the south. Sudan later retook the town. Sudan elevated the tension even further by bombing South Sudan.