CARACAS: A Venezuelan opposition election candidate was shot dead while campaigning, political leaders said Thursday, raising tensions ahead of a legislative vote that could weaken the major oil producer's socialist government.

An attacker shot Luis Manuel Diaz on Wednesday evening at an event also attended by Lilian Tintori, the wife of a jailed opposition leader and a high-profile critic of President Nicolas Maduro, the official said.

"As the rally with Lilian finished, we heard shooting ... We saw Luis fall to the ground bleeding," a regional leader of the Justice First opposition party, Abrahan Fernandez, told AFP.

Another political ally of the victim, the chairman of the Democratic Action party Henry Ramos Allup, said on Twitter that Diaz was shot at short range near the stage where he had made an appearance.

He said Tintori took refuge with security guards in a nearby shop.

Polls have indicated Maduro's government could lose its majority in the national assembly in the Dec 6 vote, potentially weakening the president's grip on power.

That has raised fears of unrest in the Latin American nation of 30 million people, already wracked by violence and an economic crisis with many families short of basic supplies.

Ramos said the shooter was believed to be a member of an "armed gang" linked to the ruling United Socialist Party of Venezuela (PSUV).

Tintori's husband Leopoldo Lopez is in prison for incitement to violence in 2014 anti-government protests, though a fugitive prosecutor in the case has cast doubt on his conviction.

That unrest left 43 people dead, according to the government.

Violence 'from highest levels'

The Union of South American Nations (Unasur) condemned Wednesday's killing and rejected "all forms of violence that could affect the normal development of the electoral process."

The 12-country regional bloc, which is sending observers to monitor the elections, in a statement called on authorities to carry out "a thorough investigation into this reprehensible act."

One of Maduro's top allies, the speaker of Venezuela's National Assembly, Diosdado Cabello, on Wednesday dismissed recent alleged attacks on opposition campaigning as "staged."

In the past two weeks, Venezuela's opposition has reported numerous assaults and harassment against its leaders including former presidential candidate Henrique Capriles, who said he was attacked by ruling-party supporters.

The opposition Democratic Unity Roundtable (MUD) coalition blamed Diaz's death on Maduro's government.

"The violent preaching from the highest levels of government is responsible for sowing hatred," it said.

It called on international authorities such as the European Union and the Vatican to urge the Venezuelan government to openly reject violence.

The PSUV had yet to react to the killing.

Venezuelans will elect 167 deputies to their single-chamber National Assembly when they vote next month.

Opinion polls indicate that the opposition is poised to win control of the body for the first time since Maduro's mentor, late leftist firebrand Hugo Chavez, came to power in 1999.

Maduro has warned that if the opposition wins, his side is "politically and militarily prepared to deal with it" and would "take to the streets."

Venezuela's oil-rich economy has suffered recently from a plunge in crude prices and runaway inflation, which have fuelled violent crime and political tension.

Venezuela has the second-highest murder rate in the world after Honduras: 54 killings per 100,000 inhabitants in 2012, according to the latest UN figures.

Political analyst Francine Jacome told AFP Wednesday's killing may have been politically motivated to instil fear, but "could have the opposite effect and encourage people to vote."

In any case, he added, "what is happening is a warning sign of violence that could break out on and after election day." — AFP