A U.N. official has intensified the call for an end to violence in South Sudan, following sustained diplomatic pressure from the African Union on South Sudanese leaders.

Adama Dieng is the U.N. secretary-general’s special adviser for the prevention of genocide. He told VOA’s South Sudan in Focus program Monday that Uganda and Kenya are contributing to the conflict.

“Although the responsibility is to protect the population in South Sudan, the timely responsibility lies with the South Sudan government; the responsibility to prevent atrocities is regional and international,” Dieng said.

He said large quantities of weapons and ammunition are flowing into South Sudan through Kenya and Uganda.

“International partners have to start targeting the accomplices, intermediaries of the South Sudanese parties.”

Representatives of the Kenyan and Ugandan embassies in Washington were not available for comment.

African Union, or AU, chairperson Moussa Faki Mahamat said Sunday that “the time has come” to impose sanctions on individuals blocking peace in South Sudan.

The U.N. diplomat said that ending the civil war in South Sudan will only be successful “if we have concerted regional and international efforts to leave no further options to the South Sudanese leaders to stop and start negotiating.”

A high-level revitalization forum led by the Intergovernmental Authority on Development, or IGAD, is scheduled to meet Feb. 5-16 in Addis Ababa to discuss security and governance structures in South Sudan.

“Now is the time to close any possibilities of alternatives,” Dieng said. “The continuation of fighting should not be left out [as a] possible option. And we need IGAD, AU Peace and Security, and the U.N. Security Council to come together and take concerted action now.”