Opposition politicians are demanding that the Venezuelan government increase its efforts to determine the fate of a group of missing miners.

More than 1,000 soldiers fanned out across the southeastern jungle state of Bolivar to search for the 28 miners who relatives say were "disappeared" and dismembered by a gang on Friday.

Francisco Rangel, Bolivar governor and a government ally, has apparently switched positions after initially accusing the opposition of politicising the event.

Willing to investigate

Al Jazeera's Virgina Lopez, reporting from Caracas on Tuesday, said that while Rangel did not have any evidence to confirm the miners' deaths, he was willing to investigate the matter.

She said the opposition is claiming the miners were killed by criminals who have control over mining deposits.

"These criminal gangs often operate in cahoots with the military. It's the only way that can explain why these gangs are so heavily armed and also seem to operate with complete impunity," she said.

Some in Bolivar think the alleged atrocity could have occurred only with the complicity of local officials [Reuters]

Families and people who say they witnessed the deadly attack have accused law-enforcement agents of participating in the crime, the Associated Press news agency said.

Americo de Grazia, a politician, said that given the number of missing miners, the reported atrocity could have happened only with the complicity of local officials.

However, Vladimir Padrino Lopez, Venezuela's defence minister, has rejected the charges.

"We know very well who is behind these accusations, and we won't fall for the provocations of the old political establishment," he said.

"We won't rest until we know everything about the incident, which is abhorrent to all Venezuelans."

READ MORE: Venezuela opposition asks neighbours to mediate in crisis

Separately, the opposition has launched a campaign aimed at toppling President Nicolas Maduro before the end of his term.

It wants to implement a three-pronged plan supplemented by a constitutional amendment reducing the presidential terms.

"The opposition claims that the government has kidnapped all of the state's institutions and that any attempts to modify the constitution would be blocked by the Supreme Court," Al Jazeera's Lopez said.

"They are saying that a change is needed and they are going all out."

Opposition to the Maduro government has grown as Venezuela's economy flounders under the weight of low oil prices and poor economic management.

Source: Al Jazeera and agencies