The Christian Solidarity Worldwide says Saw Lee Reh Kyaw was captured by Burmese forces on April 8. It says the aid worker was taken to army headquarters, where the group claims he was tortured and interrogated before being shot on April 10.
The aid worker was part of the humanitarian group Free Burma Rangers.
Two others were also captured in Karenni State, but their whereabouts are not known.
Christian Solidarity Worldwide's National Director, Stuart Windsor, says the tragic and brutal death of Saw Lee Reh Kyaw illustrates the brutality of the Burmese regime.