JUBA, Aug. 17 (Xinhua) -- About 80 incidents of aid operations were reported in July in South Sudan with most occurring in Unity and Upper Nile (41 per cent), the UN humanitarian agency said on Friday.

The UN Office for Coordination of Humanitarian Affairs (OCHA) said violence affecting humanitarian personnel and assets continued to represent the majority of incidents (60 percent).

"Two staff were killed in clearly marked vehicles in Juba and Rumbek East counties," OCHA said in its latest humanitarian report released in Juba.

"Overall, 39 percent of incidents were of a significant level of severity, over half of which involved violence against personnel or assets, including the Maban unrest, attacks on convoys, and severe lootings or compound robberies," said OCHA.

The report came barely a week after South Sudan for the third year running topped the list of most violent countries for humanitarian workers in 2017.

According to a report by Norwegian Refugee Council (NRC) released on Monday, almost one in three of the 158 major violent incidents against aid operations that took place last year occurred in the world's newest nation.

The charity said 100 aid workers had been killed in South Sudan since conflict flared in 2013, noting that those behind the attacks must be brought to justice.

According to OCHA, humanitarian access outside of Wau continued to be restricted for the second consecutive month, while extensive negotiations opened up access to Nagero and Tambura in Western Equatoria, and into central Unity after three months of inaccessibility.