A United States senator engaged in an unusual public display of anger and frustration at a session on Thursday focused on the continued fighting in South Sudan.

"I don't know how representatives of South Sudan can show up at these types of meeting without being totally embarrassed by the actions of their government," declared Bob Corker, chairman of the Senate Foreign Relations Committee.

Senator Corker addressed his remarks directly to officials of South Sudan's US embassy who were in attendance at his committee's hearing entitled "South Sudan: A Failure of Leadership."

"I don't know what kind of government you represent," the influential lawmaker told the South Sudanese diplomats.

His rebuke came in response to an acknowledgment by a US Agency for International Development official that South Sudan government forces and rebel troops have attacked humanitarian workers.

A total of 41 aid givers have been killed since the outbreak of civil war two years ago.