Venezuela's President Nicolas Maduro has received the support of Turkish President Recep Tayyip Erdogan and Argentina's football legend Diego Maradona on the eve of a controversial election opponents have denounced as a fraud.

The US, the EU and some Latin American countries have criticised Sunday's vote in which President Maduro is likely to win a second six-year term in office amid a crisis-stricken economy.

Critics have little doubt that Mr Maduro, 55, a former bus driver, is assured victory because two of his most popular opponents were banned from running and the electoral council is pro-government.

Last October, the three main opposition parties said they would boycott Sunday's election saying it would only serve what they denounced as President Maduro's dictatorship.

Any foreign support will be welcomed by Mr Maduro who has been threatened with further sanctions by the Trump administration.

US authorities have also called on Latin American countries to cut off Venezuelan officials from financial systems and restrict their travel visas.

In a conversation mired with technical problems and broadcast on Venezuelan state television, Mr Erdogan told Mr Maduro: "I have faith you will be triumphant."

Mr Maduro replied: "Venezuelans are going to give a lesson on democracy and liberty to the world on Sunday."

Like Mr Maduro, Mr Erdogan has been criticised for his authoritarian rule and his efforts to crush dissidents.

Turkey has a small presence in Venezuela but Turkish Airlines started flying to Caracas in 2016 – one of a few major international carriers to still do so.

The Venezuelan government also said Turkey would invest in its controversial "petro" cryptocurrency.

Venezuela's President Nicolas Maduro, his wife Cilia Flores and former Argentinian soccer player Diego Maradona greet supporters during a campaign rally in Caracas (Miraflores Palace/Handout)

Meanwhile, at a closing campaign event late on Thursday, Mr Maradona surprised pro-Maduro supporters gathered in the capital Caracas by dancing to the rhythm of a catchy reggaeton song while waving a Venezuelan yellow, blue and red flag.

The retired footballer and manager has previously called himself a "soldier" for Mr Maduro. He is well-known for supporting far-left politicians and was a friend of Mr Maduro's predecessor Hugo Chavez and the late Cuban leader Fidel Castro.

Under Mr Maduro's six-year-rule, Venezuela has experienced an economic meltdown and mismanagement has been blamed for the erosion of the country's once-robust oil industry leaving widespread shortages of food and medicine.

The support of President Erdogan and Mr Maradona came as a riot erupted at the country's most notorious political prison, the El Helicoide facility in central Caracas.

Videos from the prison, where hundreds of opponents to President Maduro are held, showed groups of men identifying themselves as prisoners saying they had taken over in protest against poor conditions and demanded freedom.

Human rights groups and critics of President Maduro said the government has cracked down on protests and several hundred political prisoners have been unfairly jailed.

A turbulent year in Venezuela Show all 11 1 /11 A turbulent year in Venezuela A turbulent year in Venezuela Demonstrators scuffle with security forces during an opposition rally in Caracas, Venezuela, April 4, 2017. Venezuelan security forces quelled masked protesters with tear gas, water cannons and pepper spray in Caracas after blocking an opposition rally against socialist President Nicolas Maduro. The clashes began after authorities closed subway stations, set up checkpoints and cordoned off a square where opponents had planned their latest protest against the government and the crippling economic crisis. Carlos Garcia Rawlins: "For me that was the day that made a difference, never before had I seen the protesters and police clashing men-to-men and struggling back and forward. From then, the strategy of the police changed and they never faced the protesters so close again." Reuters A turbulent year in Venezuela A man who was set on fire by people accusing him of stealing during a rally against Venezuela's President Nicolas Maduro runs amidst opposition supporters in Caracas, Venezuela, May 20, 2017. Marco Bello: "I spotted a man running in front of me as a group of protesters, most of them hooded and with makeshift shields, were chasing him so I followed them. Some 100 meters down the street, the protesters caught the man and surrounded him. When I walked up and went through the circle of people to take pictures, someone had already poured gasoline over the man and set him on fire. Reuters A turbulent year in Venezuela "Rowdy groups of government supporters busted into Venezuela's opposition-controlled National Assembly. There were several clashes happening at the same time, so I tried to follow a small group of attackers as they pushed their way through the main building. By the time I got into the building, they had already finished hitting people and were on their way out, leaving behind an opposition lawmaker covered in blood. I quickly went over to the politician, Leonardo Regnault, whose grey suit was spattered in blood. He was up against an ornate wooden door, clearly in a state of shock. Another opposition lawmaker, Luis Stefanelli, was standing next to him, hands up in a sign of surrender and pleading with the attackers to stop the beating. Reuters A turbulent year in Venezuela A member of the riot security forces points a gun through the fence of an air force base at David Jose Vallenilla, who was fatally injured during clashes at a rally against Venezuelan President Nicolas Maduro's government in Caracas, Venezuela, Reuters A turbulent year in Venezuela A demonstrators attends a rally against Venezuela's President Nicolas Maduro's government in Caracas, Venezuela, June 19, 2017. Ivan Alvarado: "I was under the highway photographing some protestors who had surrounded a woman they accused of stealing a phone from someone. I turned around to check what was happening behind me and saw this man appearing from the shadows to see what was going on. The white on his face is salt, which the protestors said helped to reduce the effects of the tear gas." REUTERS A turbulent year in Venezuela Riot security forces clash with demonstrators as a motorcycle is set on fire during a protest against Venezuelan President Nicolas Maduro's government in San Cristobal, Venezuela, May 29, 2017. Carlos Eduardo Ramirez: "Security forces arrived to disperse demonstrators that already had burned two taxis and a bus, throwing tear gas and pellets and the demonstrators' response was to throw molotov cocktails and one of those petrol bombs reached a National Guard member, setting him and the motorbike on fire." Reuters A turbulent year in Venezuela Riot security forces detain a demonstrator during a rally against Venezuela's President Nicolas Maduro's government in Caracas, Venezuela, July 28, 2017. Rock-throwing Venezuelans braved tear gas and rainstorms, blocking streets in protest against a legislative super-body to be elected two days later that critics call an attempt by President Nicolas Maduro to create a dictatorship. Carlos Garcia Rawlins: "After many hours of very violent clashes between the demonstrators and security forces, the National Guard in an attempt to end the situation, suddenly advanced their line very quickly, even going beyond where I and other photographers were taking cover. All the protesters who did not react fast enough to leave the place were detained." Reuters A turbulent year in Venezuela Opposition lawmaker Carlos Paparoni is hit by jets of water during riots at a march to the state ombudsman's office in Caracas, Venezuela, May 29, 2017. A group of young Venezuelan lawmakers has risen to prominence on the violent front line of anti-government marches that have shaken the South American country for three months, bringing 75 deaths. On the streets daily leading demonstrators, pushing at security barricades and sometimes picking up teargas canisters to hurl back at police and soldiers, the energetic National Assembly members are heroes to many opposition supporters. Carlos Garcia Rawlins: "I remember clearly how instants after I spotted Paparoni standing in front of 'The Whale', the common name of the water cannon armoured cars, he was flying through the air due to the unstoppable power of the water, as if he was a feather. Fellow protesters had to drag him out of the place, because from where I was, he seemed to have been unconscious." Reuters A turbulent year in Venezuela Flames erupt as clashes break out while the Constituent Assembly election is being carried out in Caracas, Venezuela, July 30, 2017. Deadly protests rocked Venezuela as opposition voters boycotted an election for a constitutional super-body that unpopular leftist President Nicolas Maduro vowed would begin a 'new era of combat' in the crisis-stricken nation. Carlos Garcia Rawlins: "Suddenly, a bomb exploded in the capital during an opposition protest and wounded seven police officers in what seemed to be the spread of more aggressive tactics. We were taking photos from close by but the police panicked and chased everyone away, firing teargas, rubber bullets and pellets." Reuters A turbulent year in Venezuela An injured opposition supporter is helped by volunteer members of a primary care response team during clashes with riot security forces at a rally against Venezuelan President Nicolas Maduro's government in Caracas, Venezuela, June 22, 2017. Ivan Alvarado: "This image was taken next to an airforce base where another protestor was fatally injured that day. I don't know how this man was injured, I first saw him as the first aid volunteers carried him out from the midst of the tear gas. You can really see the pain in his expression as he cries out. After I took the image the motorbike speeded off down the highway." Reuters A turbulent year in Venezuela A demonstrator shouts slogans in front of police officers during a women's march to protest against President Nicolas Maduro's government in Caracas, Venezuela Reuters

Following the riot, attorney general Tarek William Saab announced detainees would get medical check-ups before being transferred to other detention centres. Mr Saab added that US missionary Joshua Holt, who has been held in the prison for two years and pleaded for help in another video posted on social media, would not be transferred to another prison.

While there are mounting signs of Venezuela's socialist revolution being tested to its limits, President Maduro has predicted a decisive victory in this weekend's election and vowed to fight corruption and criminals he blamed for destroying the economy.

Mr Maduro has repeatedly claimed a right-wing, US-led campaign was sabotaging the economy and inciting a coup to establish a capitalist leadership.

Addressing a crow of supporters on Thursday, Mr Maduro said he had stayed loyal to Mr Chavez's legacy, adding: "I will dedicate my life to fixing the economy of this country. My spirit is renewed, my energy recharged."

Opposition lawmaker and economist Angel Alvarado told Reuters the government no longer cared about being seen as legitimate in Western eyes, but instead was looking to cement relations with countries like Turkey, Russia, China and Qatar.

China and Russia have provided Mr Maduro's government with billion-dollar loans and both countries control significant oil fields in Venezuela.

Mr Maduro will still be facing two candidates in Sunday's election: Henri Falcon, of Progressive Advance, and independent Javier Bertucci.

Venezuelan opposition candidate Henri Falcon of the Avanzada Progresista party, said he wanted to free the country from dictatorship (REUTERS/Marco Bello)

Mr Falcon is a lawyer and former governor of Lara State who abandoned Mr Maduro's PSUV party in 2010 and has since distanced himself from the "Chavismo" movement of his one-time mentor, President Chavez, a tactic that has not entirely convinced his critics.

During his final rally, Mr Falcon told a cheering crowd of supporters: "I will free Venezuelans from dictatorship. Maduro, the people want to bid you good riddance because you have caused great harm."

Mr Bertucci is an evangelical pastor and businessman who says he offers "the light among the darkness", despite opposing abortion and adoption for LGBT+ couples.