South Sudan's then-Vice President Riek Machar, left, looks across at President Salva Kiir, following the first meeting of a new transitional coalition government on April 29, 2016. (Jason Patinkin/AP)

South Sudan’s former first vice president and top opposition leader has fled the country, according to a spokesman, making the prospect of a sustainable peace in the world’s youngest country even more remote.

More than a month after the country’s most recent spasm of violence, Riek Machar has arrived in a “neighboring country,” according to a Facebook post from his spokesman James Gatdet Dak. A news release from another spokesman, Mabior Garang, late Wednesday called the move an evacuation and said it followed a “botched attempt to assassinate” Machar.

Garang said Thursday that Machar crossed the border into Congo and was airlifted to the capital, Kinshasa, according to the Associated Press. Machar was planning to travel to Ethiopia soon, the report said, citing the spokesman.

The split between Machar and President Salva Kiir in 2013 prompted the country’s long descent into civil war, which has left tens of thousands dead. The war has divided much of the country along ethnic lines, with Kiir’s predominantly Dinka troops fighting against Machar’s Nuer followers.

Last year, the two agreed to an internationally brokered peace deal, and Machar returned to the capital city of Juba earlier this year with about 3,000 armed men. But last month the feud between the two sides again spiraled into a broader conflict, consuming Juba for days and leaving hundreds dead.

Now Machar’s absence from South Sudan casts further doubt on the resumption of a peace process between the two sides. Without his support or his return to Juba, it’s unlikely that any negotiation will end successfully. Some experts worry that his self-imposed exile might embolden the Machar forces who remain in the country, as they give up hope of reconciliation. Indeed, officials in the Yei region have reported recent clashes between the two groups.

The United States and other members of the international community spent more than two years trying to persuade Machar and Kiir to reconcile. That looked unlikely even before the recent outbreak of violence. The two had a long-standing rivalry that had grown more bitter as they clashed over the spoils of the federal government — including many millions diverted from international assistance programs.

The fighting in July showed just how much bitterness remained. According to analysts, Kiir’s men tried to hunt down and kill Machar after he fled Juba. Many of his Nuer supporters remain in U.N. displacement camps. During last month’s fighting, 217 women in Juba were sexually assaulted, according to the U.N. human rights chief, Zeid Ra’ad al-Hussein. Most of the victims were members of the Nuer ethnic group, and most of the attackers were members of Kiir’s forces — the official army of South Sudan.

The U.N. Security Council voted this month to send 4,000 additional peacekeepers to South Sudan — about 13,000 are already there — in recognition of the deteriorating situation. But the peacekeepers have been able to do little to prevent the country from sliding back toward war.

“The over-focus on a new peacekeeping mandate at the expense of political developments in the country reflects international disunity and a lack of political strategy,” the independent International Crisis Group said Tuesday in a report.

During the fighting last month, Machar fled the capital, not disclosing his location. Weeks later, Kiir formally replaced him as first vice president with Taban Deng Gai, a former Machar ally. That appointment has created challenges for the international community, including the United Nations, which has been careful in meeting with Gai so as not to validate Kiir’s dismissal of Machar.