Aid workers in South Sudan are being attacked with greater frequency, a consortium of aid groups here said Wednesday.

There have been 37 robberies at aid agency compounds in the just last 90 days, said Brian McDonald, information manager for the NGO Forum. The NGO Forum's members are increasingly concerned about the safety of their staff, the consortium said in a statement Wednesday.

"We call on the South Sudan authorities to take the necessary steps to ensure the safety and security of NGO staff and assets in Juba and elsewhere in South Sudan," the statement said.

Last Thursday, robbers shot and killed Rombek Paul Mori of the group Action Against Hunger in a daytime break-in at the agency's compound in the capital, Juba.

Mori is the 30th aid worker killed in South Sudan since fighting broke out in 2013 between government troops loyal to President Salva Kiir and rebel forces led by former Deputy President Riek Machar.

Two female international aid workers reported being robbed and raped in Juba on September 6, according to an internal U.N. security report seen by The Associated Press.

Many aid workers in Juba live in high-walled compounds and are required to adhere to curfews at night. Earlier this year, the government passed a bill criticized by aid groups as restricting their activities.

Kiir and Machar signed a peace deal last month but both sides have since accused each other of launching attacks.