Environmental activist Homero Gomez, who fought to protect the famed monarch butterfly has been found dead in Mexico's western state of Michoacan, a local authority said on Wednesday, two weeks after he disappeared.

It was not immediately clear how Gomez had died but his disappearance sparked an outcry in an increasingly violent country where activists are routinely threatened, harmed or even killed as a result of their work.

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The Human Rights State Commission of Michoacan reported his disappearance on January 13 when commission official Mayte Cardona told Reuters news agency: "He was probably hurting the interests of people illegally logging in the area".

Michoacan's attorney general confirmed Gomez's death.

One source at the state attorney's office, who declined to be named, told Reuters the cause of death had not been determined but that an initial review had found no signs of torture.

Activists said his death could be related to disputes over illegal logging, water or income from visitors' fees.

Homero Aridjis, an environmentalist and poet who is a longtime defender of the butterfly reserve, called the death of Gomez "worrisome."

"If they can kidnap and kill the people who work for the reserves, who is going to defend the environment in Mexico?" Aridjis said.

Urging the protection of their habitat, the reserve El Rosario Ocampo Michoacan, Gomez became best known among Mexicans for posting mesmerising videos and photos of the orange and black butterflies on social media.

Millions of these butterflies make a 2,000 mile (3,220 kilometre) journey each year from Canada to spend winter in central Mexico's warmer weather. However, the insects are facing new challenges linked to extreme weather and changing habitat.

Michoacan state is home to the country's largest monarch butterfly reserve, a World Heritage Site, as well as many rival drug gangs who battle to control smuggling routes through often-arid terrain to the Pacific and the interior of the country.

The butterflies need healthy tree cover to protect them from rain and cold weather.

Mexico has clamped down on illegal logging, which was once a significant threat to the reserves, but which has fallen to about one-third of last year's level. But there have been reports of increased "salvage" logging of supposedly sick trees.

Disputes over water from mountain springs have also occurred in the region and avocado planters have long coveted the area, which has near-ideal growing conditions for the valuable fruit.