A UN representative in Costa Rica sent condolences Monday to the family of a slain environmentalist who volunteered for a turtle protection group and had reported threats by criminal groups.

The body of Jairo Mora Sandoval, 26, was found face-down and handcuffed Friday next to the car he was driving in Limon, on the Caribbean coast, police told AFP.

"The United Nations sends its sincerest condolences to the family, friends and colleagues of (Mora Sandoval), and recognizes his noble work on behalf of protecting turtles which are an essential part of Costa Rica's and the world's biodiversity," said a statement released here by UN resident coordinator Yoriko Yasukawa.

Mora Sandoval monitored nesting turtles, recording the number of nests and trying to rescue eggs with a program that was entirely volunteer-based and dependent on donations.

He had complained in a La Nacion newspaper report published in April that the area's environmentalists were threatened by criminal organizations apparently because those engaged in looting turtle nests are linked to drug traffickers.

The US Embassy in Costa Rica called the killing "senseless" in a post on its Facebook page that also hailed Mora Sandoval as a committed environmentalist.