MALAKAL, Sudan,(Reuters) – A land mine has killed one child and injured four in a south Sudan town, the latest in a string of blasts prompting authorities to threaten U.N. mine clearers with expulsion from the area, officials said.

The series of blasts have been in Malakal in south Sudan, which is riddled with mines. The difficult terrain means it could take years to remove all unexploded ordnance left from more than two decades of civil war — Africa’s longest.

“We have ordered them (deminers) to either start their work and finish it as soon as possible, or they leave the town immediately,” deputy governor of the large town of Malakal, Dok Jok Dok, said late on Wednesday.

The land mine exploded in a southeastern suburb of Malakal town, killing one child instantly and seriously injuring four others between the ages of 8 and 13.

“One child out of the five who were blown up by the mine unfortunately died and the rest — we don’t know whether they will survive,” said a doctor in Malakal hospital who declined to be named.

Malakal was a garrison town for the northern government during the bitter north-south civil war which claimed 2 million lives.

U.N. mine clearance workers said they had already begun work but their priority was to clear humanitarian routes to access the millions who need food and medical aid in the south, rather than Malakal town itself.

“We are not mandated to remove all the mines and unexploded ordnance from Malakal and the surrounding areas in the short term,” said Adam Wheeler, operations officer for the U.N. mine action service.

He confirmed they had been told to begin work in the town or leave, but said he had not received official documentation to that effect.

The mine explosion on Saturday was the 11th incident in Malakal town in the past eight months, where most of the victims have been children. Fifteen have been killed and more than 20 have had limbs amputated.