(CNN) -- A Rwandan opposition politician was found dead Wednesday after he went missing the day before, according to an official with the Democratic Green Party of Rwanda.
Andre Kagwa Rwisereka, deputy-president of the party, was last seen alive by his sister Monday night, and was planning to make his way to the Rwandan capital of Kigali for a meeting Tuesday, said Frank Habineza, the party's president.
Rwisereka's car was found abandoned Tuesday, Habineza said. His car and house keys and driver's license were inside, but there was no sign of him.
Rwisereka's body was found by residents in a wetland area about 3 kilometers from the city of Butare and 2 kilometers from the National University of Rwanda, Habineza said. Rwisereka's head was nearly severed from his body, he said.
The body was taken into police custody, and an investigation is under way, Habineza said Wednesday, but no arrests had been made.
Habineza said both he and Rwisereka had been receiving death threats since February, but he said the police have not provided them with protection.
"We are very threatened as a party and as individuals," he said. "We are scared. We are also sad about the demise of our colleague."
The party, launched in 2009, is aimed at bringing about "a real, genuine and authentic political opposition in the country," according to its website.
The party "is a people's party, striving for a progressive people's democracy, the type of democracy that will ensure all Rwandans are able to freely live in their country without fear and enjoy all their rights ... DGPR strives for a Rwanda that is at peace with itself and its neighbors, the continent of Africa and the international community."
Journalist Naisenya Leposo contributed to this report for CNN.