Security in South Sudan could deteriorate "rapidly and unpredictably," London has warned

The UK has advised British nationals to leave South Sudan, where escalating tensions have sparked widespread fears that the East African nation is on the verge of renewed civil war.

The British Foreign, Commonwealth, and Development Office (FCDO) issued an updated travel advisory on Thursday, warning that security in Africa's youngest country "could deteriorate rapidly and unpredictably."

"If you are in South Sudan and judge it safe to do so, you should leave now. If the unstable security situation deteriorates, routes into and out of South Sudan may be blocked. Juba airport may close or be inaccessible," the foreign office stated.

The alert comes a day after the British embassy in South Sudan's capital, Juba, announced that it has temporarily reduced its staff and suspended in-person consular services due to security threats. The US has taken similar measures, ordering non-emergency US citizens, including government personnel, to depart the volatile country. Germany and Norway have also temporarily closed their embassies in South Sudan. Berlin has said the African country, which gained independence from war-torn Sudan in 2011, is "once again on the brink of civil war."

The landlocked country has remained unstable since the end of a five-year civil war that erupted in 2013 over a feud between its president, Salva Kiir Mayardit, and his current first vice president, Riek Machar.

READ MORE: Germany shuts embassy in African state over civil war fears

Tensions have been growing between President Kiir and Machar since several Sudanese soldiers were recently killed when a UN helicopter came under attack while attempting to evacuate them from the troubled Upper Nile state, where clashes erupted in March. The South Sudan People's Defense Forces are fighting the White Army militia, which is primarily made up of Nuer people, the vice president's ethnic group.

On Wednesday, Machar's party reported that over 20 heavily armed vehicles "forcefully" entered the vice president's residence, disarmed his bodyguards, and issued an arrest warrant for him "under unclear charges."

Later on Thursday, the opposition group said authorities had placed Machar under house arrest, adding that the action has effectively collapsed a 2018 peace agreement that ended the 2013 civil war.

The UN has also warned that the vice president's arrest "takes the country yet one step closer to the edge of a collapse into civil war and the dismantling of the peace agreement."