The rendezvous in Ethiopia's capital Addis Ababa represents the latest international effort to end more than four years of civil war in the world's youngest nation.

Tens of thousands have been killed and millions have been driven out of their homes and into starvation.

Kiir and Machar will meet at the invitation of Ethiopia's prime minister, Abiy Ahmed, who also chairs the Intergovernmental Authority on Development (IGAD) regional bloc that has taken the lead in thus-far fruitless peace negotiations.

Abiy "will call upon the two leaders to narrow their gap and work for the pacification of South Sudan and relieve the burden of death and uprooting of South Sudanese people," said Meles Alem, a spokesman for Ethiopia's foreign ministry.

Kiir's attendance was confirmed by South Sudan's ambassador to Ethiopia, James Pitia Morgan.

Manasseh Zindo, a senior official in Machar's Sudan People's Liberation Movement-in Opposition rebel group, said Machar would attend.

IGAD first proposed the meeting last month after the most recent unsuccessful round of peace talks.

Sudanese President Omar al-Bashir suggested hosting the two foes in Khartoum, an offer Machar rejected, while Kiir's government said it would prefer to have the meeting outside the region altogether.

- Failed peace -

The two men have been central to the fate of South Sudan since its 2011 separation from the north.

The country descended into civil war in 2013 after Kiir accused Machar, his former deputy, of plotting a coup against him.

They have not met since July 2016, when heavy fighting in the capital, Juba, signalled the collapse of a 2015 peace deal forcing Machar to flee to South Africa.

The renewed violence spread across the country, spawning numerous new armed opposition groups and further complicating peace efforts.

Efforts to revitalise the 2015 agreement resulted in a ceasefire in December which lasted just hours before warring parties accused each other of breaking it.

Tens of thousands have died and nearly four million South Sudanese have been driven from their homes by the conflict which the United Nations ranks among the most serious humanitarian crises in the world.

Forty-eight percent of the population are experiencing extreme hunger and seven million will need aid this year, according to the UN.

International patience with the conflict has worn thin. Last month, the UN Security Council gave the two warring sides a month to reach a peace deal or face sanctions.

The United States has also grown increasingly frustrated with Kiir's government.

Washington was a critical backer of South Sudan during its separation from Sudan, and remains Juba's biggest aid donor.

A top American official earlier this month threatened parties on both sides of the conflict with sanctions after a report from US foundation The Sentry said South Sudanese elites were profiting from human rights abuses.

Despite the pressure, observers say Kiir has little incentive to make concessions to his rivals.

His soldiers are winning militarily, while the opposition is more fractured than ever before.