South Sudan's First Vice-President Riek Machar has been charged with murder, treason and crimes against humanity in a move that some fear could reignite the country's civil war.

Justice Minister Joseph Geng Akech said the charges against Machar relate to an attack in March by a militia allegedly linked to the vice-president, which killed 250 soldiers and a general.

Machar's spokesperson has condemned the move as a "political witch-hunt".

The roads leading to Machar's house in the capital, Juba, have been blocked by tanks and soldiers.

Forces loyal to Machar fought a five-year civil war against those backing President Salva Kiir until a 2018 peace deal ending the fighting in the world's newest country.

Machar has been under house arrest since March, with the UN, African Union and neighbouring countries all calling for calm.

Seven others have been charged alongside Machar, including Petroleum Minister Puot Kang Chol and Army Deputy Chief of Staff Lt Gen Gabriel Duop Lam, Justice Minister Joseph Geng Akech said in a statement.

They are all Machar allies who were arrested at the same time as him and have also been in detention ever since. Another 13 suspects remain at large, the minister said.

Machar and Chol have also been suspended from their government roles, according to an announcement on state TV.

Machar's spokesperson Puok Both Baluang said the whole crisis had been fabricated by Kiir's allies and was "designed to dismantle the peace agreement".

He further said that South Sudan's judicial system was not independent, "operating instead as politically directed courts".