Violence is taking center-stage in the run-up to the Venezuelan election after a politician, Luis Manuel Diaz, secretary of the opposition Democratic Action party, was gunned down at a poll campaign event in the town of Altagracia de Orituco in central Venezuela Wednesday.

The opposition and several international organizations have blamed the killing on the ruling party, which in turn has threatened to sue for defamation.

The event where Diaz was killed, was also attended by the wife of Leopoldo Lopez, a high-profile government opponent who is serving a lengthy prison sentence and who said she was near Diaz when the shooting occurred and that she may have been the target of the attack.

The general secretary of Democratic Action, Henry Ramos Allup, said the shots were fired by armed groups belonging to the ruling United Socialist Party of Venezuela, adding violence by such groups against activists, candidates and opposition events were on the rise.

Meanwhile, the head of the government's legislative election campaign, Jorge Rodriguez, said Thursday the slain local opposition leader was the member of a criminal gang who was being investigated for homicide since 2010.

He said it was a known fact that Diaz had "links with construction trade unions" and was allegedly fighting "for Union control of the area" with a member of another opposition party Justice First.

Rodriguez also said a complaint will be filed with the Attorney General's Office against Ramos for slander and added Diaz's killers have been identified and the police was looking for them.

Earlier, Venezuelan President Nicolas Maduro too had said the killing points to a gang clash and brushed aside statements by Secretary General of the Organization of American States, Luis Almagro, who said the incident was meant to intimidate the opposition.

Almargo also asked the Venezuelan government to act quickly to ensure the upcoming Dec.6 elections are not "an exercise of force, violence and fear," because "the killing of a political leader is a mortal wound to democracy."

Maduro said he expected a rectification from Almagro once the investigation into the incident was through.

Meanwhile, the European Union Thursday asked Venezuela to expedite investigation into the murder.

Amnesty International too urged urgent inquiries into the incident for fear it would leave "the door open to more violence" in the run up to the elections.

United States too condemned the killing, calling it the "deadliest of several recent attacks and acts of intimidation aimed at opposition candidates."