At least 19 people have been killed in South Sudan, including an American freelance journalist, after fighting broke out between government troops and rebel forces in the southern part of the country, rebel leaders and the military said.

Christopher Allen, who worked with various news outlets, including Al Jazeera in the past, was killed in heavy fighting in the town of Kaya in Yei River State on Saturday.

"On the ground, about 16 [bodies] have been found around the defensive position of the SPLA including this white man," military spokesman Santo Domic Chol told Reuters news agency, referring to the SPLA national army.

Three government soldiers were also killed, he said.

READ MORE: The work of Christopher Allen

Rebel forces identified the man found as Allen, who had embedded with them for the past week, along with two other journalists.

"We are sad for his family. He came here to tell our story," one rebel fighter, who asked not to be named, said.

He added that Allen had been in the middle of the fighting and wearing a jacket marked 'PRESS'.

The US embassy in the country confirmed that Allen had been killed and that his family had been notified.

RIP Christopher Allen. Thankful for all journalists, South Sudanese and expats, dedicated to covering atrocities occurring in 🇸🇸. Stay safe https://t.co/cxOWarFEf2 — Dominic Lucero (@DominicFLucero) August 26, 2017

After gaining independence from Sudan in 2011, South Sudan descended into war in December 2013, pitting President Salva Kiir's troops against those or rebel leader and former Vice President Riek Machar.

A peace accord was signed in August 2015 and Machar returned to the capital in April last year to share power with Kiir, before the deal fell apart less than three months later and Machar and his supporters fled the capital.

Tens of thousands of people have been killed and more than 3.5 million have been displaced since the conflict began.

The war has created what has been called the world's fastest-growing refugee crisis and both sides of the conflict have been accused of abuses.