Nicaragua’s authoritarian leaders, Daniel Ortega and Rosario Murillo, are poised to extend their rule over the crisis-hit Central America country with an election that opponents and much of the international community have denounced as a charade.

Ortega, the Sandinista rebel who led Nicaragua during the 1980s and has governed continuously since 2007, will seek an unprecedented fourth consecutive term in Sunday’s contest, which follows a ruthless six-month political crackdown on rivals.

Seven presidential contenders have been thrown in jail or placed under house arrest since May, while other leading critics have fled to Costa Rica, the US and Europe, and foreign journalists have been barred from the country.

In recent weeks, reporters from CNN, Le Monde, New York Times, NPR, Washington Post and the Honduran newspaper El Heraldo have all been prevented from entering Nicaragua to witness proceedings.

On Sunday night the US president Joe Biden denounced what he called “a pantomime election that was neither free nor fair, and most certainly not democratic”.

“Long unpopular and now without a democratic mandate, the Ortega and Murillo family now rule Nicaragua as autocrats, no different from the Somoza family that Ortega and the Sandinistas fought four decades ago,” Biden added in a statement.

Tiziano Breda, a Central America specialist at Crisis Group, said Ortega’s assault on Nicaragua’s beleaguered opposition meant there was little doubt over the election result, which is expected to be announced in the early hours of Monday.

“[Ortega losing] would be quite a plot twist – but I don’t see it happening,” said Breda, predicting that the former leftwing guerrilla, who helped rescue Nicaragua from dictatorship in the 1970s, would secure between 60% and 70% of the vote.

Breda believed the repression was driven largely by Ortega’s fear of losing power and being prosecuted for a deadly 2018 crackdown on student-led protests in which hundreds were killed.

“He has shown that political survival outweighs any possible internal or external pressure. It was a matter of life or death for him to ensure re-election on Sunday,” Breda said.

Jesús Tefel, an exiled political activist who fled to Costa Rica in July after a succession of allies were jailed, described the election as a “farce” and urged the international community to do more to help re-establish Nicaragua’s battered democracy.

“What we have now in Nicaragua is a dictator and a dictatorial system, which is trampling over every single one of our rights. It’s like the perfect dictatorship,” he said of Ortega and Murillo, his powerful vice-president and wife.

“This is an awful precedent for global democracy. The message it sends is that you can be a dictator and there are no consequences. This will encourage other dictators – it will encourage the enemies of democracy,” said Tefel, a leader from the opposition group Unidad Nacional Azul y Blanca (Unab).

Zoilamérica Ortega Murillo, Ortega’s estranged stepdaughter, condemned the election as “an absurdity, a stitch-up and a form of virtual reality”.

“A war on truth is under way,” Ortega Murillo, who cut ties with Nicaragua’s leaders in 1998 after accusing Ortega of sexual abuse, said during an interview in Costa Rica where she also lives in exile.

Speaking to the Spanish magazine Alfa y Omega, Ortega’s former vice-president, the exiled writer and one-time Sandinista Sergio Ramírez, said: “Daniel Ortega will decide the number of votes he secures.”

Ortega and Murillo have defended the wave of detentions, claiming the targets were criminals guilty of crimes “against the homeland” and seeking to topple their Sandinista administration with a foreign-backed coup.

In a rambling televised address on Sunday afternoon, Ortega said Nicaraguan voters had a choice between the peace and economic stability he offered and the “terrorism, confrontation and war” promoted by his opponents. “This is a historic battle,” Ortega declared, claiming the overwhelming majority of Nicaraguans wanted the former.

Despite such hardline rhetoric, Breda suspected Nicaragua’s leaders would change tack after the election. So far, Ortega has been focused on guaranteeing victory by bullying the opposition into submission. After securing a fourth term, Breda predicted he would try to calm the situation and placate the international community by proposing a “dialogue” with members of the opposition and business community.

“I expect a shift in tactics, because they will serve a different goal after 7 November,” Breda said. “I think he’s aware that he will need to seek a governability settlement with some sectors which are crucial for the functioning of the state and for the overall economic stability of the country.”

Thousands of exiled Nicaraguans were expected to march through the streets of Costa Rica’s capital, San José, on Sunday to protest against what many see as Nicaragua’s transformation into a police state.

Ana Quirós, a feminist campaigner and former Sandinista who was among the organisers, said she was convinced that sooner rather than later Nicaragua would experience political change.

“I have patience, I have hope and I have confidence,” said Quirós who was stripped of her Nicaraguan nationality and deported for backing the failed 2018 rebellion.

Quirós admitted unity was a challenge given the ideological and personal differences between Ortega’s foes. “I have sat down with people who I spent so many years battling, people from the right, people who are anti-abortion,” she said. “But before we can discuss our differences we need to resolve this situation and that means first of all securing the release of the political prisoners.”

Ortega and Murillo have shrugged off criticism of the election. Asked to comment claims of irregularities, Nicaragua’s vice-president reportedly sent a one-word email to the Washington Post: “Gracias!”