The United States, Britain and Norway are warning South Sudan's warring sides to respect a cease-fire after reported violations.

The statement by the three countries on Tuesday comes after the armed opposition and South Sudan's government traded accusations of violations of the cease-fire that began early Dec. 24.

South Sudan's civil war has entered its fifth year, with untold tens of thousands killed.

The troika's new statement says field commanders "and their political superiors" will be held accountable for cease-fire violations.

It also calls on all sides to allow unrestricted humanitarian access. Millions in the East African nation are in need of aid but the United Nations and others have repeatedly expressed frustration at obstacles to its delivery.