An indigenous environmental activist was killed in Morelos, Mexico Wednesday, three days before a referendum on the construction of a gas pipeline and two thermoelectric plants that he had organized to oppose, the Associated Press reported.

Samir Flores Soberanes had challenged the words of government representatives at a forum about the so-called Morelos Comprehensive Project a day before his murder, The Peoples in Defense of Land and Water Front (FPDTA), the group Soberanes organized with, said in a statement.

"This is a political crime for the human rights defence that Samir and the FPDTA carried out against the [project] and for people's autonomy and self-determination," the group said in a statement reported by The Guardian.

The Morelos state government, however, challenged whether Soberanes' murder was politically motivated. State prosecutor Uriel Carmona said that the murder was not related to the upcoming referendum and that investigators were considering the involvement of organized crime.

Soberanes and the FPDTA opposed the energy project, which would have run a pipeline through Soberanes' home village of Amilcingo, because of concerns about how it would impact the health, safety and water of the largely indigenous communities in the surrounding area, the Associated Press reported.

Newly elected Mexican President Andres Manuel López Obrador called the murder "vile" and "cowardly," but said the vote would take place when planned.

"I'm very sorry about the murder," López Obrador said, as the Associated Press reported. "The consultation we have to continue because it is a process that was already agreed to."

The FPDTA said Soberanes had been murdered Wednesday morning around 5 a.m. after two vehicles parked outside his home. The people inside the vehicles called to him to come out and then shot him when he emerged.

Soberanes was an indigenous Náhuatl, a community radio producer and a human rights activist, The Guardian reported.

The project he opposed was first proposed in 2011, but had been recently taken up by López Obrador as a means of reducing electricity prices. The new president has also called for referendums on major projects like a new Mexico City airport and a train in southern Mexico. The airport project was defeated and the train, between Cancun and Tulum, was approved, The Associated Press reported.

The FPDTA wrote a letter to López Obrador warning him that the referendum would lead to violence in their community.

López Obrador promised to address the frequent murders of human rights and environmental activists in Mexico. However, he also made remarks about civil society Tuesday that concerned some activists, calling it "conservative" for opposing his projects and planning to militarize the police.

"All those who oppose the [project] … we are for López Obrador radical ultra-conservatives," FPDTA told The Guardian.