The East African organization leading peace talks on South Sudan says that rebels were a no-show on the second day of negotiations.

The regional bloc IGAD called on the rebel delegation "to honor its commitment to resolve the crisis" and return to the negotiating table, which were to continue Wednesday.

Elsewhere, aid leaders in South Sudan said Wednesday they are horrified by the killings of at least six South Sudanese aid workers earlier this week.

Toby Lanzer, the top U.N. aid official in the country, said the aid community demands that armed groups stop targeting civilians and respect aid workers. He said several colleagues in Upper Nile state, where the killings occurred, are still in danger.

South Sudan saw violence spiral across the country beginning last December.