JUBA (Reuters) - Gunmen ambushed a convoy of buses and other vehicles traveling on a major highway in South Sudan on Thursday, killing at least 14 passengers and wounding 35, police said.

The unknown gunmen attacked the convoy as it drove toward Juba on a highway linking the South Sudan capital with Nimule, on the country’s southern border with Uganda.

The ambush happened in an area called Moli, 140 km (85 miles) from the capital, even though the convoy was escorted by members of a joint army and police force that guard convoys traveling in the dangerous region.

“At around 11 am, the convoy of buses and other vehicles coming from Nimule heading to Juba fell into an ambush near Moli village,” Brigadier-General Daniel Justin Boulogne, a South Sudan police spokesman, said.

“The shooting happened at the first car of our organized force. The attackers opened fire on them and four vehicles were burned. We have confirmed 14 people were shot and 35 others wounded,” he said.

The attackers fled as the security escort returned fire.

Boulogne said authorities were still working to establish an official casualty list.

Police do not know how many people were in the convoy in all, he said.

South Sudan, the world’s youngest country, has been mired in civil war since President Salva Kiir dismissed his deputy Riek Machar, in 2013.

In April 2016 the United States and other Western nations backed a peace accord that saw Machar return to the capital and again share power with Kiir.

But the deal fell apart less than three months later and Machar and his supporters fled the capital, pursued by helicopter gunships.

The fighting has forced more than three million people from their homes and has increasingly followed ethnic lines, leading the United Nations to warn of potential genocide.