Official for Spain's ruling Socialists sent to prison for corruption

Former transport minister José Luis Ábalos has also been implicated in the investigation into kickbacks for public contracts, which has created the biggest political crisis Sanchez has faced since taking office in 2018.

The sources said a Supreme Court judge ordered the detention of Cerdán, who has only recently quit as the Spanish Socialist Workers' Party organisation secretary -- the ruling party's number three post -- as there was a "risk" he might try to flee or destroy evidence.

He is being held without bail on allegations of corruption, money laundering and criminal association, the sources said.

Cerdán denied the accusation in an audience with the lead investigating judge on Monday, saying he was the victim of a political plot, they said.

Sánchez has sought to distance himself and the Socialist party from the scandal, which involves suspicions of dirty dealings in the purchase of health equipment during the Covid-19 pandemic.

"The Socialist party reacted firmly from the start," the prime minister said.

"Santos Cerdán was dismissed" from the party when the revelations emerged, he added when questioned about the case at an international conference in Seville.

A police report has said there was evidence including audio recordings suggesting Cerdán received payments in exchange for irregularly awarded public contracts.

Ábalos, the prime minister's former right-hand man, and a top adviser, Koldo García, are also among the suspects targeted in the investigation.

Sánchez has repeatedly apologized over the case and denied knowledge of the alleged scheme.

But the opposition has called for the prime minister to resign.