UPDATE 4-South Sudan accuses Sudan of air strike on refugee camp
* Sudan's army denies it carried out the attack
* Border region violence has raised tensions
* South Sudan president warns of Sudan's "pending invasion" (Adds details on fighting in South Kordofan)
By Hereward Holland
YIDA CAMP, South Sudan, Nov 10 (Reuters) - A refugee camp in South Sudan's Unity state was bombed on Thursday, South Sudan officials and witnesses said, threatening to raise tensions with Sudan in the violence-plagued border region.
Taban Deng, the governor of Unity state, accused Sudan of carrying out the attack. "These people (Khartoum) should be taken to book. They should adhere to international laws and regulations," he told reporters in Bentiu.
Sudan's armed forces denied they carried out the strike. In a statement before the bombing, South Sudan's president Salva Kiir talked of Sudan's "pending invasion" of its neighbour.
Violence along the poorly defined border since South Sudan's independence in July has strained ties between the two former civil war foes. They have accused one another of backing rebel groups on their sides of the border.
A Reuters correspondent heard a large explosion in the Yida refugee camp, then saw a crater about two metres (6.6 feet) wide, an unexploded bomb wedged in the side of a school building and a white aircraft flying north. Witnesses said there were three further explosions at 3 p.m. (1200 GMT). Continued...