Venezuelans headed to the polls on Sunday to vote in a presidential election in which incumbent President Nicolas Maduro is aiming to secure a third term against rival Edmundo Gonzalez Urrutia.

Long queues of voters gathered at various ballot stations even ahead of the polls opening at 6 a.m. (1000 GMT), the French news agency AFP reported. Polls are due to remain open until 6 p.m.

Around 21 million Venezuelans are registered to vote. Tens of thousands of security forces have been deployed, with border control ramped up and public gatherings and protests banned.

Ahead of the vote, US Secretary of State Antony Blinken said Washington would not prejudge the results of the election, yet called on parties to respect the democratic process which will be closely watched.

Maduro against biggest 'Chavismo' threat

The vote pits 61-year-old Maduro against 74-year-old former diplomat Gonzalez Urrutia, who is considered the biggest ever threat to "Chavismo." The populist movement was founded by Hugo Chavez, the incumbent's predecessor and mentor.

Independent polls suggest Maduro is lagging behind Urrutia in terms of voter support, but the incumbent president is relying on the loyalty of state institutions to pull off a win.

Maduro, who is accused of locking up and harassing his critics amid growing authoritarianism, urged Venezuelans to "Vote, vote, vote, and peace will triumph," in a social media message overnight.

He vowed to ensure the results of the vote would be respected after he cast his poll on Sunday. Days ahead of the vote, Maduro had said that the outcome of the vote would determine whether the coming period would be one of "peace or war."

"If they do not want Venezuela to become a bloodbath, a fratricidal civil war produced by the fascists, let us guarantee the greatest success, the greatest electoral victory of our people," he said at a rally.

His contender Gonzalez Urrutia meanwhile called on his compatriots to turn out in large numbers "to transform your future" in what "will undoubtedly be the most important democratic expression of the people in recent years."

"We hope and wish that everything will transpire in peace," he said in a video posted on social media.

The opposition contender was selected in April to represent a coalition of opposition parties at the last minute, after powerhouse Maria Corina Machado was blocked from competing for 15 years, following a court ruling.

After voting on Sunday, Urrutia said he was "prepared to defend until the last vote," amid rising tensions in his electoral challenge.

Lack of transparent oversight

There is growing concern regarding the independence of the elections, especially after Caracas blocked international observers and held up a plane carrying four ex-presidents of Latin America who had planned to monitor the vote.

Earlier in May, Venezuela rescinded an invitation to European Union observers to monitor the presidential vote.

Maduro's government had reached a deal with the opposition last year to hold elections with international observers present.

A Venezuelan NGO meanwhile accused the government on Friday of holding 305 "political prisoners" and arresting 135 people linked to the opposition campaign since January.

For months, the government has carried out an arrest campaign targeting politicians, journalists and rights activists, which Caracas claims are related to plots and conspiracies against Maduro.

Venezuela has been under tough US sanctions for years, with many in the country hoping for change. Most Venezuelans live on merely a few dollars a month, amid biting fuel and electricity shortages and crippled health care and education systems.

The government, which enjoys support from Cuba, Russia and China, blames sanctions, but many observers say corruption and mismanagement are to blame.

rmt/wd (AFP, AP, Reuters)