The United States has ordered all its non-emergency staff in South Sudan to leave, amid rising tensions in the country.

Fighting in recent days has threatened an already fragile peace deal between President Salva Kiir and Vice-President Riek Machar.

The two leaders signed a peace agreement in 2018 to end a five-year civil war that killed hundreds of thousands of people, but their relationship has remained fraught.

On Sunday, the US State Department said that fighting was ongoing in South Sudan between various political and ethnic groups and that "weapons are readily available to the population".

"Due to the risks in the country, on March 08, 2025, the Department of State ordered the departure of non-emergency US government employees," it said.

The UN human rights commission for South Sudan on Saturday warned of an "alarming regression" that threatened to undo years of progress towards peace.

President Kiir has called for calm and made an assurance that the country would not return to war.

In an escalation of the tensions, a UN helicopter that had been evacuating members of the national army was shot at on Friday, killing several people, including one crew member.

Earlier in the week, the deputy chief of the army and two ministers allied to Machar were arrested by security forces, which an opposition spokesman termed a "grave violation" of the peace deal.

The arrests of the Machar-allied officials followed clashes in the country's Upper Nile state between government forces and a militia known as the White Army, which had fought alongside Machar during the civil war.

South Sudan, the world's newest nation, gained independence in 2011 after seceding from Sudan.

But just two years later, following a rift between Kiir and Machar, the country descended into a civil war, in which more than 400,000 people were killed.

The 2018 power-sharing agreement between the two stopped the fighting, but key elements of the deal have not been implemented – including a new constitution, an election, and the reunification of armed groups into a single army.

Sporadic violence between ethnic or local groups has continued in parts of the country.