The former Spanish prime minister José Luis Rodríguez Zapatero has been placed under investigation for alleged influence-peddling and other offences by a judge examining the state bailout of a Venezuela-linked airline during the Covid pandemic.

Zapatero, a socialist who served as prime minister from 2004 to 2011, has been ordered to appear before Spain’s highest criminal court, the Audiencia Nacional, on 2 June.

Although other former and serving Spanish prime ministers have been called to testify in corruption cases, this is the first time a former prime minister has been placed under criminal investigation.

The latest investigation is part of an inquiry into the €53m (£46m) state rescue of the Spanish airline Plus Ultra in March 2021. Prosecutors are examining whether the company made “inadequate use” of the public funds the government approved for the bailout, while anti-corruption police are investigating whether the airline used the rescue money to launder funds from Venezuela through France, Switzerland and Spain.

In a statement released on Tuesday, the court said a judge had authorised police to search Zapatero’s office as well as those of three other companies.

“Audiencia Nacional judge José Luis Calama has ordered former prime minister José Luis Rodríguez Zapatero to appear as a suspect on 2 June on charges of influence-peddling and related offences,” the statement said.

It said Calama had lifted secrecy restrictions relating to the proceedings and had accepted jurisdiction after a lower court recused itself in favour of the Audiencia Nacional.

Zapatero, who denies any wrongdoing, appeared before a senate committee in March, where he said he “had never taken any commissions from Plus Ultra”. But he did acknowledge doing some consultancy work for his friend Julio Martínez Martínez, a businessman who worked with Plus Ultra and who was arrested by anti-corruption officers in December last year.

Appearing before the senate committee in February, Plus Ultra’s president, Julio Martínez Sola, insisted that bailout had been conducted in complete compliance with the relevant laws. “There was no exceptional procedure outside the norm; there was no preferential treatment or undue interference; there was no illicit aid,” he said. “There was a regulated process, with controls, reports, and very strict conditions that have been met. Nobody has given us anything for free.”

Zapatero’s socialist successor as prime minister, Pedro Sánchez, is facing a series of corruption allegations involving his family, his party and his administration.

Last month, Sánchez’s wife, Begoña Gómez, was charged with embezzlement, influence-peddling, corruption in business dealings and misappropriation of funds at the end of a two-year investigation by a judge in Madrid. The prime minister’s younger brother, David Sánchez, is also facing trial this month on charges of influence-peddling.

Both Gómez and David Sánchez deny any wrongdoing, and the prime minister has accused his political and media opponents of smearing and pursuing his family.

Two senior former figures in Sánchez’s government are on trial for alleged corruption. The prime minister’s former right-hand man, the former transport minister José Luis Ábalos, is accused – along with his former aide Koldo García and the businessman Víctor de Aldama – of taking kickbacks on public contracts for sanitary equipment during the Covid pandemic. Ábalos and García, who deny all charges, are facing sentences of 24 years and 19 years respectively while Aldama, who has already admitted to his part in the alleged scheme, faces a seven-year sentence.

The socialist party issued a statement in support of Zapatero on Tuesday, calling him a pioneering prime minister whose “two terms were defined by an ambitious programme to expand rights, equality, and social protection”. It added: “The right and the far right have never forgiven him for these advances.”

The opposition conservative People’s party described Zapatero’s as “Sánchez’s muse” and said, “the principle that links Spain’s two most recent socialist prime ministers is corruption … this indecency must end”.