(CNN) -- Sudan has arrested foreigners in the disputed region of Heglig, its defense ministry said Saturday, the latest in the spiraling conflict between the Sudans.
Those arrested were identified by the defense ministry as British, Norwegian, South African and South Sudanese.
"They were engaged in suspicious activities, collecting war debris," it said.
Meanwhile, a South Sudanese military spokesman reported ongoing clashes and bombings -- though a Sudanese military spokesman denied any such attacks.
Col. Philip Aguer, a spokesman for the Sudan People's Liberation Army of South Sudan, said eight bombs were dropped in Unity state Saturday.
Friday, "Khartoum-supported mercenaries" attacked an SPLA position in a town called Wau, causing 21 deaths, he said. Three fighters were captured alive, he added.
The SPLA seized three trucks, which are said to belong to the Sudanese Armed Forces, said Aguer, vowing to retaliate against "all these acts of aggression."
But Al-Sawarmi Khalid, a spokesman for the Sudanese Armed Forces, said, "We have not bombed Wau, or any other place in South Sudan."
South Sudan split from Sudan last year as part of a 2005 peace deal that ended decades of war in Africa's largest nation. The war left 2 million people dead and ended with the peace agreement that included an independence referendum for the south.
Despite the split in July, unresolved issues remain between the two, including status of their citizens, division of national debt, disputed border areas and sharing of oil wealth.
Simmering tensions peaked this month when South Sudan seized the oil-producing region of Heglig from Sudan, raising the stakes by targeting a resource that fuels the economies of both nations.
Heglig oil facilities account for about half of Sudan's production of 115,000 barrels a day.
Sudan claims ownership for the region, and lodged complaints with the United Nations and the African Union to pressure South Sudan to withdraw troops from its territory.
A day after South Sudan withdrew from the disputed region, it accused Sudan of launching ground and aerial attacks on its territory.
CNN's Kim Chakanetsa and journalist Isma'il Kushkush contributed to this report.