UNITED NATIONS, March 27 (Xinhua) -- UN Secretary-General Antonio Guterres is deeply concerned with the escalating situation in South Sudan, warning that the country is on the brink of civil war, his spokesman said on Thursday.

The statement came following reports of the house arrest of South Sudanese First Vice President Riek Machar in the capital of Juba on Wednesday night.

The UN Mission in South Sudan (UNMISS) calls on all parties in the country to "exercise restraint and uphold the Revitalized Peace Agreement (RPA)," said Stephane Dujarric, spokesman for the UN chief, at a daily briefing.

The peacekeeping mission is joining other regional and international peace partners in expressing alarm at the detention under house arrest of Machar, Dujarric said.

Dujarric said the United Nations warns that the confinement "takes the country yet one step closer to the edge of a collapse into civil war and the dismantling of the 2018 peace agreement."

UNMISS head and special representative of the secretary-general, Nicholas Haysom, issued a statement late Wednesday after reports of the detention.

"This will not only devastate South Sudan but also affect the entire region," he said. "Tonight, the country's leaders stand on the brink of relapsing into widespread conflict or taking the country forward towards peace, recovery and democracy."

UNMISS urged President Salva Kiir and the first vice president to resolve grievances, end the military confrontation, uphold the RPA and take the country forward together towards a peaceful and democratic future.

There were reported clashes between government troops of the South Sudan People's Defence Forces and the Sudan People's Liberation Army in Opposition near Rejaf, just south of the capital Juba, and in Wunaliet, to the west.

Dujarric said it should be clear to all that the people of South Sudan can ill afford to endure the consequences of the civil war. "It's vital that the leaders of the country put the interest of the people first and foremost," he stressed. ■