UNITED NATIONS (AP) — The U.N. Security Council called Monday for a halt to fighting in South Sudan and swift deployment of a new contingent of 4,000 peacekeepers to boost the existing U.N. force in the conflict-wracked African nation.

The U.N.'s most powerful body backed Secretary-General Antonio Guterres' efforts to reinvigorate the peace process in the world's newest nation, beef up the 12,000-strong U.N. peacekeeping force and prevent the security situation from deteriorating.

The council statement, which also urged access for humanitarian aid, followed a closed-door meeting between the 15 council members and the top monitor of South Sudan's peace deal, former Botswana President Festus Mogae.

Britain's U.N. Ambassador Matthew Rycroft warned of "the threat of continued violence," which U.N. special envoy on the prevention of genocide Adama Dieng has said "could slip into genocide."

Rycroft said the phrase that stuck in his mind from Mogae's briefing was: "one step forward, two steps back."

"I think that was a sign that things are very difficult in relation to the political agreement," he told reporters.

There were high hopes that South Sudan would have peace and stability after its independence from neighboring Sudan in 2011. But the country plunged into ethnic violence in December 2013 when forces loyal to President Salva Kiir, a Dinka, started battling those loyal to Riek Machar, his former vice president who is a Nuer.

A peace deal signed in August 2015 has not stopped the fighting, and clashes last July between forces loyal to Kiir and Machar set off further violence throughout South Sudan. The conflict has killed tens of thousands of people and forced 3.1 million to flee their homes.

The Security Council decided in August to send an additional 4,000 peacekeepers after clashes the previous month killed hundreds in South Sudan's capital Juba. South Sudan initially objected to the force and has delayed its deployment.

Earlier this month, the government claimed the council mandate to boost the existing force expired on Dec. 15 — but the U.N. mission responded that the mandate was extended until December 2017.

Sweden's U.N. Ambassador Olof Skoog, the current council president, said members strongly support a "truly inclusive national dialogue" in South Sudan and regional and African Union efforts to achieve a political solution.

The council also stressed the importance of ending impunity and encouraged the African Union's efforts to establish a hybrid court in the country.