Seventeen miners murdered near a gold deposit were mainly shot in the head, and four suspects have been arrested so far in a case that has shocked Venezuela, the chief state prosecutor said on Wednesday.

The killings have shone a light on long-running gang wars in the vast and remote jungle area near the borders of Guyana and Brazil that is littered with illegal mines.

President Nicolas Maduro's government has blamed local gangs, with the involvement of foreign paramilitaries, while the opposition has accused local security forces of complicity.

The miners disappeared on March 4, prompting days of protests by relatives and families in Tumeremo town, before their bodies were discovered this week in a mass grave.

"They were all executed with guns ... 16 in the head and one in the thorax," chief prosecutor Luisa Ortega told reporters.

Four people have been arrested with links to the murders or to the presumed leader of the gang that perpetrated them, she added. An Ecuadorean man believed to be the mastermind is also being sought.

Opposition politicians have cited relatives and witnesses as saying up to 28 miners may have been killed, but the prosecutor said the confirmed total was 17. She also ruled out earlier reports that the bodies had been mutilated with a chain saw.

Awash with guns and plagued by ever-larger and better-armed gangs, Venezuela has one of the world's highest homicide rates.