GENEVA, April 11 (Reuters) - The United Nations warned on Friday that forces in Sudan could attack a refugee camp in South Sudan because it was being used by armed groups, an assault that would rekindle tensions between the oil-producing neighbours.
An unidentified aircraft circled Yida camp, in South Sudan's border state Unity, this week, raising fears of a strike, Melissa Fleming, spokeswoman for the U.N. High Commissioner for Refugees (UNHCR), told journalists in Geneva.
South Sudanese fighters ended decades of conflict with the Sudanese government with a peace deal in 2005 that paved the way for South Sudan to split away as an independent country six years later.
But sporadic clashes over disputed territory have continued and Sudan has regularly accused its neighbour of harbouring and arming rebels along their long border. South Sudan dismisses the allegation.
South Sudan's Yida camp shelters tens of thousands of people who have fled bombings and clashes between rebels and Khartoum government forces in South Kordofan region, on the Sudanese side of the border.
But it was proving hard to make sure all the camp residents were civilians, the UNHCR said, and the appearance of the aircraft on Wednesday had heightened tensions.
"The sighting raised fears that the refugees' settlement may soon come under direct or indirect military attack," said Fleming.
Pressed on whether the aircraft was a Sudanese government plane, she declined to speculate, adding: "Having a refugee camp with 70,000 people, where you have elements that should not be in a refugee camp, could draw this kind of attack from across the border."
"If we see military elements in a refugee camp, the danger is that these elements can draw conflict into the camp, that they can turn the refugee camp into a target," Fleming added.
She said the plane was spotted two days after local officials reported a suspected military aircraft had dropped more than five bombs over Neem, a settlement in South Sudan on a route used by people traveling from the war-torn Nuba Mountains of South Kordofan in Sudan.
The agency had since encouraged refugees to move away from Yida and the volatile border to another camp, but many were reluctant to do so, she said.
Yida, close to the disputed and "highly militarised" Jau corridor separating the two countries, was bombed twice in November 2011, UNHCR said, without spelling out who was responsible.
Millions of people died in the decades-long war between South Sudanese fighters and the Khartoum government, a conflict fuelled by ethnicity, oil and ideology.
South Sudan has itself collapsed into civil conflict since its independence, forcing more than a million people to flee its territory.
Landlocked South Sudan, an impoverished country about the size of France, has to use a Sudanese pipeline to get its crude to market. But distrust remains deep between the two countries and many of the disputes that drove their long war have not been resolved.
(Reporting by Stephanie Nebehay and Tom Miles; Editing by Andrew Heavens)