A woman who campaigned against the expansion of coal-fired power plants in the Philippines has been killed, police said Monday, the latest death in one of the world's deadliest nations for environmental activists.

Gloria Capitan, 57, was shot in the head on Friday as she sat in her family's karaoke bar, police said, adding no suspects had been caught.

Greenpeace condemned the killing, saying it was yet another example of environmental defenders being murdered for standing up to powerful interests.

The Philippines is the second most dangerous country in the world for environment activists, with 33 killed last year, Global Witness said in a report last month.

Critics have long said that the country suffers from a "culture of impunity," where powerful figures believe they can kill opponents and critics without fear of being punished.

Capitan was the leader of a local group that campaigned against the expansion of coal interests in Mariveles and Bataan province, some 60 kilometers (37 miles) west of Manila.

"(Capitan's death) seems to be really related to her work in opposing the coal storage facility in Mariveles and the expansion of coal-fired power plants in Bataan," said Reuben Muni, a climate and energy campaigner with the Philippines branch of Greenpeace.

As of 2014, coal accounted for at least 31 percent of the Philippines' power supply, according to the government's energy department.

This proportion is likely to grow as more coal-fired power plants are built to cope with the surging demand for power.