South Sudan's vice president, Riek Machar, has been charged with treason and crimes against humanity, the Justice Ministry said Thursday.

The charges against Machar stem from an attack on a military base in Nasir in March, during which more than 250 soldiers were killed.

He has been under house arrest since then, deepening the divide between him and President Salva Kiir.

Fragile power-sharing between Kiir and Machar

South Sudan became independent from Sudan in 2011.

But after just two years of independence, Kiir, an ethnic Dinka, dismissed Machar, an ethnic Nuer, as vice president.

A civil war erupted that was largely fought along ethnic lines and saw some 400,000 killed.

Kiir reinstated Machar as first vice president under the terms of a 2018 peace deal that was never fully implemented.

Their partnership has remained tenuous, and sporadic violence has continued between their respective factions.

Puok Both Baluang, a spokesman for Machar, said the latest charges "constitute a political witch hunt" and that the justice system lacks independence and can be politically directed.

Justice Minister Joseph Geng Akech said the charges send a clear message: "Those who commit atrocities against the people of South Sudan, against our armed forces, and against humanitarian personnel will be held accountable, no matter their position or political influence."

In addition to Machar, 20 others were indicted in the case, including seven senior government officials. Charges include treason, murder, conspiracy, terrorism, destruction of public property and military assets, and crimes against humanity.

What happened at the Nasir base?

A militia from Machar's ethnic Nuer community, known as the White Army, took over the Nasir base in early March, killing senior officers, including a general.

A UN helicopter was shot at during a rescue operation, and a pilot was killed.

The United Nations, which operates a major peace-building mission in South Sudan, said at the time that the country was "witnessing an alarming regression that could erase years of hard-won progress."

Edited by: Louis Oelofse