“The young nation of South Sudan has enough problems without these horrific weapons, which kill and keep on killing long afterward,” said Steve Goose, arms division director at Human Rights Watch (HRW) and chair of the Cluster Munition Coalition (CMC).
“The governments involved should quickly find out who is behind this and make clear they will be held responsible,” he said in a statement.
The UN Mine Action Service (UNMAS) found up to eight cluster bomb remnants and an unspecified number of unexploded submunitions, called "bomblets", by a stretch of road 10 miles (16 kilometers) south of Bor, in an area "not known to be contaminated" before fighting broke out in South Sudan in mid-December, HRW said."The UN experts concluded that this was a recent use of cluster bombs, because they have been up and down this road in the past," Human Rights Watch Deputy Director Leslie Lefkow said.
Bor has changed hands at least four times in clashes between the Sudan People’s Liberation Army (SPLA) and opposition forces.
The Uganda People’s Defense Force (UPDF) has been supporting South Sudan’s government forces, including with air power, HRW said.
Both South Sudanese and Ugandan forces have the capacity to drop the types of cluster munitions found near Bor, while, "As far as we know, the opposition forces in South Sudan do not have air capacity,” Lefkow said.
UN Secretary-General Ban Ki-moon last week condemned the use of cluster bombs in the South Sudan conflict, but has not indicated who the UN believes was responsible.
Both Juba and Kampala have denied using cluster bombs, which are banned by an international treaty to which Uganda is a signatory.
Uganda’s army spokesman Paddy Ankunda said he would welcome an investigation into the use of the banned munitions in South Sudan, adding that Uganda was not responsible for the use of the bombs near Bor.
“We don’t have cluster bombs. We don’t intend to possess them and we have not used them anywhere. Let them investigate," Ankunda said.
Cluster munitions are designed to explode in the air, sending shrapnel over a wide area. Eighty-four countries have ratified the 2008 convention prohibiting the use, production, transfer and stockpiling of the weapons.
Lefkow said the cluster bomb remnants found near Bor are particularly dangerous because they can still be triggered weeks after they were dropped, which potentially puts civilians at risk as they return to their homes.
Bonifacio Taban and Karin Zeitvogel contributed to this report from Kampala and Washington D.C.