Panama has accused the Venezuelan government of blocking a flight carrying former Latin American leaders who were due to observe presidential elections on Sunday.

Panamanian President José Raúl Mulino said on social media that Venezuela had denied the plane permission to take off as long as the former leaders were aboard. The Venezuelan government has rejected the allegations.

Among those on the plane were the ex-presidents of Mexico, Panama, Costa Rica and Bolivia – all critics of the current Venezuelan government who said they were hoping for an opposition victory.

Venezuelan President Nicolás Maduro, who is seeking a third consecutive term, has said he will win “by hook or by crook”.

“The aircraft was denied permission to take off from Tocumen as long as they remain on board,” Mr Mulino wrote on X, referring to Panama City’s airport.

Vicente Fox, Mexico’s former president, posted a video on social media from the airport, in which he said: “Nicolas Maduro has caused all Copa flights heading to Caracas and Venezuela to be suspended.”

“A bad sign for Sunday,” he said separately, in a radio interview. “We were removed from the plane with blackmail and pressure from Venezuela.”

Others on board included Miguel Ángel Rodríguez of Costa Rica, Jorge Quiroga of Bolivia and Marta Lucía Ramírez, former vice-president of Colombia.

Panamanian Foreign Minister Javier Martínez-Acha said that Venezuela had “blocked the airspace of its country to Copa Airlines” for “several hours” – a claim denied by Venezuelan authorities.

Last year, Mr Maduro agreed to allow international observers to be present in this election, resulting in a temporary easing of US sanctions.

However last week, Venezuela issued a decree restricting travel across the country’s border from Friday, a move it said was intended to protect the election.

But there have been a string of similar crackdowns, prompting concern that Venezuela is blocking access to international observers.

The chair of the National Electoral Council, government ally Elvis Amoroso, uninvited EU officials who had been due to watch the vote.

And Colombian officials, Spanish MPs and Chilean senators all reported being denied entry at Caracas Airport.

Spanish People’s Party president Alberto Núñez Feijóo said the Venezuelan government “does not want the international community to have eyes and ears in Venezuela this weekend”.

Mr Maduro’s PSUV party has ruled for 25 years, but opposition activists hope to unseat the president on Sunday.

The main opposition parties have united behind one candidate, Edmundo González.

Most opinion polls suggest he has an overwhelming lead over Mr Maduro but he fears the vote will not be free and fair and that the government may not concede defeat.