They said aid workers “need to be able to deliver services without interference and fear of violence. They should never be a target”.
The Heads of Mission of the US, the Netherlands, the UK, Germany, France, Sweden, Norway, Switzerland, Canada, Ireland, and the EU issued the joint statement.
The statement comes after the killing of two aid workers in Pibor area. The offices of two non-governmental organisations were also set alight in Renk town.
Nine humanitarian workers have so far been been killed this year in South Sudan.
A total of 124 aid workers, mostly South Sudanese, have lost their lives in the line of duty since conflict erupted in the country in late 2013.