The BBC quoted him to have said that the incident took place when the northern armed forces were pursuing Darfuri rebels near the border. A northern army spokesman confirmed that troops had engaged the rebels, but said the fighting had taken place 23km (14 miles) north of the border.

The spokesman said he did not believe a bomb had landed in the south. The United Nations confirmed a bombing had occurred and said it was sending a team to assess the situation.

Tensions in Sudan have been rising in recent weeks, ahead of a referendum next year on possible independence for the south of the country - a consequence of peace deal in 2005 that ended a long civil war.