Sudan denies carrying out cross-border bombing of a site housing refugees from two of its conflict-torn states.

A refugee camp in South Sudan’s Unity state has been bombed, officials and witnesses say, in a development that threatens to raise tensions between the two former civil war foes, South Sudan and Sudan.

There were no immediate reports of casualties at the Yida camp, less than 25km from the border with Sudan, following Thursday’s apparent bombing..

Taban Deng, the governor of Unity state, blamed the Khartoum government over the incident.

“These people [Khartoum] should be taken to book. They should adhere to international laws and regulations,” he said in Bentiu, a town 654km northwest of Juba, the capital of South Sudan.

The UN confirmed that an attack had been carried out in the area where about 20,000 refugees are camped after fleeing violence in Sudan’s South Kordofan and Blue Nile states, where opposition groups have been fighting Sudan’s army since June.

“We can confirm that at least two bombs were dropped near Yida refugee camp, with an as yet unknown number of

casualties,” the spokesman for Ban Ki-moon, the UN secretary-general, said in a statement.

Al-Sawarmi Khalid, a spokesman for Sudan’s armed forces, said they had not bombed any site in South Sudan’s territory.

“South Sudan is a state in the United Nations. We respect international law, and it’s impossible that we would do that,” he said.

Large explosion

Yida, the camp apparently bombed, shelters refugees fleeing violence in two states across the northern border

A Reuters correspondent heard a large explosion in Yida on Thursday, then saw a crater about two metres wide, an unexploded bomb wedged in the side of a school building and a white aircraft flying north.

Fire could be seen in the dry grass around the crater about 100 metres away from an aid agency compound in the refugee camp.

“They [Khartoum] don’t want any life in the Nuba mountains, and now they are expanding the war to the South Sudan

republic,” Yousif Ismail, a refugee from the Nuba mountains, said as he stood by the hole.

The US strongly condemned the attack and urged both sides to resume negotiations to prevent the violence escalating into a full-scale conflict.

“These provocative aerial bombardments greatly increase the potential for direct confrontation between Sudan and South Sudan. The United States demands the government of Sudan halt aerial bombardments immediately,” Jay Carney, the White House press secretary, said in a statement.

“This bombing of civilians and humanitarian workers is an outrageous act, and those responsible must be held accountable for their actions.”

The Khartoum government, for its part, reported fresh clashes in South Kordofan on Thursday.

Khalid said Sudanese forces fought opposition groups in South Kordofan about 5km south of the town of Taludi, killing dozens and destroying a tank and other military vehicles.

‘Pending invasion’

Violence along the poorly defined border since South Sudan’s independence in July has strained ties between the Juba and Khartoum governments. They have accused one another of backing armed groups on their sides of the border.

Last week, Sudan submitted its second complaint to the UN Security Council, accusing South Sudan of supplying

anti-aircraft and anti-tank missiles, ammunition, landmines and mortars to fighters in South Kordofan and Blue Nile.

Salva Kiir, the South Sudan president, denied those claims in a statement on Thursday, calling them “smokescreens to mask Khartoum’s own activities in support of the armed dissident groups that are fighting its proxy war against the Republic of South Sudan”.

The accusations were being used to justify Sudan’s “pending invasion of the South”, Kiir said.

Fighting has also broken out in Sudan’s Blue Nile state this year. Blue Nile and South Kordofan are home to tens of thousands of fighters who sided with the south during the war but were left in Sudan when South Sudan seceded, analysts say.

South Sudan split off into a separate country in July after voting overwhelmingly for secession in a January referendum, the culmination of a 2005 peace deal that ended decades of war between north and south.

About two million people died in the north-south civil war, waged for all but a few years since 1955 over religion, ideology, ethnicity and oil.