Honduran police have arrested four people in connection with the killing of environmental and indigenous rights activist Berta Cáceres, including an employee of a company whose project she helped block, the attorney general's office said on Monday.

Cáceres, 43, who fought to stop the construction of hydroelectric plants and mines on indigenous territory, was fatally shot in La Esperanza, Honduras, in early March, sparking domestic and international outrage.

One suspect was a communications manager at Desarrollos Energeticos, or DESA, a local company behind the Agua Zarca hydroelectric project that Cáceres was able to get halted after mobilizing residents and activists, the attorney general's office said.

DESA did not reply to Reuters' requests for comment.

Two of the other suspects were soldiers, one on active duty and the other now retired, a spokesman for the armed forces, Lenin Gonzalez, told reporters.

Honduran President Juan Orlando Hernández congratulated the investigators and reiterated his pledge to see justice served. But prosecutors have yet to put forward an official explanation for what motivated the killing.

Cáceres, who had previously received death threats, won the Goldman Environmental Prize in 2015 for her efforts to prevent the construction of a $50 million dam that threatened to displace hundreds of indigenous people.