Spain's former Socialist Prime Minister José Luis Rodríguez Zapatero has been placed under investigation for influence peddling and related crimes, a court said Tuesday.

Zapatero, who served as prime minister from 2004 to 2011, has been summoned to testify on June 2nd, Spain's top criminal court said in a statement.

The case centres on the bailout of Venezuela-linked airline Plus Ultra during the Covid-19 pandemic - years after Zapatero had left office. The airline received a €53 million ($62 million) public loan in March 2021 from a government fund set up to support strategic companies hit by the crisis.

The rescue of Plus Ultra sparked controversy in Spain, with opposition parties questioning the airline's financial situation and its links to Venezuela.

This is the first time that a former Spanish prime minister has been placed under formal investigation since the country returned to democracy following the death of long-time dictator Francisco Franco in 1975.