Prime Minister Pedro Sánchez has apologised to the Spanish people after an escalating corruption scandal brought down a senior Socialist party colleague.

Sánchez, who has led Spain since 2018, said there was no such thing as "zero corruption", adding he was wrong to trust Santos Cerdán, the secretary of his party and close political colleague.

Cerdán has been asked to testify in court after a judge suggested he may have acted with former party officials in improperly awarding public contracts in exchange for kickbacks.

He said on Thursday he was stepping down to defend himself in the Supreme Court on 25 June, maintaining he had "never committed a crime nor have I been complicit one".

Amid mounting speculation over his own future, the prime minister called a news conference in a bid to distance himself from the creeping scandal. He said he knew absolutely nothing about the corruption affair and instead pledged to restructure the leadership of his Socialist PSOE party.