Indigenous activists in Myanmar’s Karen state are mourning the killing of a community leader who campaigned for a peace park to protect a local forest and its residents’ land rights.

Saw O Moo was ambushed by government troops on 5 April as he was riding a motorbike with a soldier from the Karen National Liberation Army (KNLA), a rebel group that is fighting for autonomy.

The military has claimed both men were plain-clothes rebels “suspected of sabotage” who were armed with grenades at the time of the shooting, according to the Irrawaddy newspaper.

But colleagues who worked with Saw O Moo say he was a peaceful campaigner who had simply given a ride to the KNLA soldier.

“He was a civilian, and the allegations by the Tatmadaw (Myanmar military) that he was a plain clothes soldier are blatant lies,” said Hsa Moo, media coordinator for the Karen Environmental and Social Action Network, which works for indigenous rights in the region.

Saw O Moo worked for the network for 12 years and was involved in the campaign to create a “Salween Peace Park”. This is a bottom-up initiative by the Karen people to protect their culture, land and wildlife. Spanning 5,400 sq km in the Salween river basin, it covers the habitats of Asiatic black bear and Sunda pangolin, which are threatened by mercury pollution from goldmines and the Hat Gyi hydroelectric project.

The government has never recognised the peace park, which is near an area of skirmishes between the state military and the KLNA. More than 2,000 people have recently been forced from their homes by the upsurge in conflict, which locals say has been driven by government offensives.

On the day of his death, Saw O Moo had reportedly been organising humanitarian aid for the displaced people. Fellow activists say the KLNA soldier he took for a ride – Hser Blut Doh – had been on guard duty at the village. He escaped unharmed during the shooting, but the area remains so tense that the dead man’s family have reportedly been unable to reclaim his body.

In a tribute, fellow campaigners remembered Saw O Moo “for his lifelong passion and commitment to preserving indigenous Karen cultural traditions, promoting customary land stewardship, and leading local community forest conservation activities”.