CARACAS, Venezuela (AP) — Venezuelan authorities launched an investigation yesterday into the shooting death of an Indian chief who campaigned for the demarcation of indigenous lands.

Information Minister Ernesto Villegas said Sabino Romero, a leader of the Yukpa tribe, was fatally shot on Sunday along a highway in the western state of Zulia.

Villegas said investigators suspect Romero may have been the victim of a hired killing, but authorities have not determined a motive.

"The investigation is under way," Villegas said. "We cannot put forth any type of hypothesis regarding this reprehensible act."

The Prosecutor General's Office issued a statement saying that Romero reportedly was gunned down by two assailants wearing ski masks and riding motorcycles. The gunmen stopped a vehicle carrying Romero and sprayed it with bullets, according to prosecutors.

The indigenous leader's wife, Luisa Martinez de Romero, was wounded.

No suspects have been arrested.

Justice Minister Nestor Reverol told state television federal police travelled from Caracas to Zulia to aid local authorities investigating Romero's murder.

Reverol suggested that owners of large swaths of land located along the Perija mountain range may be responsible for Romero's murder.

Romero had long campaigned for the rights of the Yukpa and the demarcation of their lands in the Perija mountain range bordering neighbouring Colombia.

Foro por la Vida, a group of Venezuela's most prominent human rights organisations, in a statement strongly condemned the killing, calling for "exhaustive, transparent and quick investigation" to determine who was responsible.

In a statement of its own, Foro por la Vida noted that tensions between the Yukpa and cattle ranchers have increased in recent years, occasionally leading to violence, as the Indians have settled on lands claimed by ranchers and demanded the government initiate the demarcation of their ancestral lands.

Land owners are suspected of killing several tribe members amid land-related disputes, according to human rights organisations. Rights groups said the Yukpa repeatedly denounced threats from ranchers, but authorities failed to act.

"There's a lot of tension in the region," said Lusbi Portillo, an Indian rights activist, told The Associated Press in an interview.

Portillo counts at least eight murders involving Yukpa tribe members in recent years.

"There are no investigations, nobody is arrested," added Portillo, a representative of Sociedad Homo et Natura, a non-governmental organization that closely tracks indigenous rights issues in Venezuela.

Portillo said that he has received anonymous death threats by telephone.

Romero's father, Jose Manuel Romero, was killed in 2009. Tribe members blame a local rancher for his slaying, but the alleged aggressor was never arrested or faced criminal charges, according to Portillo and human rights activists.