A Brazilian environmentalist has been shot dead, days after gunmen killed an American nun who campaigned to protect the Amazon rain forest from loggers and ranchers vying for its natural resources.

Authorities said Wednesday that Dionisio Ribeiro was shot in the head late Tuesday at the Tingua nature reserve near Rio de Janeiro.

Colleagues say Mr. Ribeiro had received death threats for some time because of his efforts to stop poaching and the illegal felling of palm trees.

Mr. Ribeiro's murder follows the recent shooting deaths of Sister Dorothy Stang, an environmental activist and advocate for the poor, and Daniel Soares da Costa, an advocate of landless peasants.

Brazilian police have arrested a man suspected of being an intermediary between gunmen and a local rancher accused of ordering Sister Dorothy's killing.

Some information for this report provided by AF and Reuters.