JAKARTA (Reuters) - Separatist rebels in Indonesia’s Papua province who killed a group of workers building a bridge this month have rejected government calls to surrender and instead demanded a referendum to decide the future of the area.

Security forces have launched an operation to hunt down members of the military wing of the Free Papua Movement (OPM), which claimed responsibility for killing at least 16 workers and a soldier in the mountainous Nduga area.

The OPM has said it viewed the men as members of the military and casualties in a war against Indonesia’s government. Indonesian officials said the workers were civilians.

Papua, the resource-rich western part New Guinea island, has been plagued by a violent separatist conflict since the former Dutch colony was incorporated into Indonesia after a widely criticized U.N.-backed referendum in 1969.

In a video posted on YouTube on Monday, OPM spokesman Sebby Sambom read an open letter to President Joko Widodo in which he dismissed calls on their military wing, known as the West Papua National Liberation Army (TPNPB), to surrender and start dialogue.

Standing behind the banned separatist Morning Star flag, Sambom demanded Widodo hold another referendum for native Papuans to decide whether they want to be integrated with Indonesia.

“TPNPB will not surrender under any circumstances before the independence of the nation of Papua is realized from Indonesian occupation,” Sambom said.

“The war will not stop before the demands of the TPNPB are carried out by the government of Indonesia.”

He called for unrestricted access to Papua for foreign journalists and for the U.N. refugee agency and the international Red Cross to help take care of civilians caught up in the conflict.

Sambom confirmed to Reuters on Tuesday the authenticity of the video.

A spokesman for President Widodo did not immediately respond to a request for comment.

In 2017, a senior government official, in response to a petition to the United Nations for a new referendum, said Papua was a legal part of Indonesia and already incorporated through a referendum process.

The OPM had accused the military of killing civilians in its operations which it said included bombings.

Chief Security Minister Wiranto rejected that accusation but said soldiers did use grenades in clashes.

Two soldiers were wounded on Tuesday and three separatists had been killed in clashes, the military said.

Since coming to power in 2014, Widodo has tried to ease tension in Papua by freeing prisoners, addressing rights concerns and stepping up investment, including through a Trans Papua road.