“I am deeply saddened by this senseless act and send my deepest condolences to the family, friends and colleagues of Sister Veronika Racková,” said the humanitarian coordinator, Eugene Owusu, in a statement issued by the UN Office for the Coordination of Humanitarian Affairs (OCHA). “I welcome steps being taken by the authorities to bring the perpetrators to justice and urge them to act swiftly.”

The health worker was driving an ambulance in Yei, in southwest South Sudan, on her way back from a medical centre when she was attacked. Her death brings the number of aid workers killed in South Sudan since the beginning of the conflict in December 2013 to 54.

“Violence against humanitarian workers and humanitarian assets is categorically unacceptable and must stop,” said  Owusu. “I urge the Transitional Government of National Unity to endeavour to strengthen the safety and security environment for aid workers and will work intensively with them to achieve this.”