The heads of the United Nations and African Union are warning South Sudan's warring sides to immediately stop violating a cease-fire or face "consequences."

The joint statement by Antonio Guterres and Moussa Faki Mahamat comes after South Sudan's government and armed opposition traded multiple accusations of attacks since the cease-fire came into effect on Dec. 24.

The international community has shown growing signs of impatience with both sides as civil war in the world's youngest nation enters its fifth year with untold tens of thousands killed.

The new statement, noting "appalling suffering," also calls on all sides to protect civilians and allow humanitarian access to a nation where millions are going hungry.

Further peace talks mediated by a regional bloc are expected in early February in neighboring Ethiopia.