ADDIS ABABA, Ethiopia — South Sudan’s warring factions on Thursday signed a new agreement to cease hostilities and protect civilians in the latest effort to calm a devastating civil war. The cease-fire is set to begin first thing Sunday morning, or Christmas Eve.

They also agreed to grant humanitarian access to conflict-affected areas after days of talks in neighboring Ethiopia brokered by the Intergovernmental Authority on Development regional bloc.

South Sudan is entering its fifth year of civil war, and no one knows how many tens of thousands of people have been killed in the world’s youngest nation. Parts of the East African country are on the brink of famine, and well over a million people have fled abroad.

The United States called the deal ‘‘the last chance for the implementation of the peace process.’’ Past attempts at peace deals have failed amid renewed violence.

South Sudan’s government is under growing pressure to find an end to the civil war as the United States and others threaten further sanctions.

‘‘This is a gift to South Sudanese people to celebrate their Christmas and New Year. This is the most precious gift of all time,’’ Ethiopia’s foreign minister, Workineh Gebeyehu, said during a ceremony. ‘‘But as past experience has showed, implementation is the longer and more difficult aspect. Many critical issues lie ahead.’’

ASSOCIATED PRESS