Spain's former conservative prime minister Mariano Rajoy on Monday denied any knowledge of an alleged spying operation inside his own party.

Rajoy was answering questions from a parliamentary committee investigating accusations that officials inside Rajoy's Popular Party (PP) launched a spying operation on a senior party official.

"I never had any knowledge of the existence of this operation..., so I gave instructions on something I knew nothing about," he said.

"I don't know what they were looking for."

The alleged operation targeted former treasurer, Luis Barcenas, who at the time was at the centre of a probe into a kickbacks scheme within the party. Barcenas was later jailed for 33 years over that affair.

The aim of the alleged spying was to find out what dirt Barcenas had on party officials.

Investigators are investigating the possibility that the alleged operation might have been led by Jorge Fernandez Diaz, who at the time served as Rajoy's interior minister.

Pressed by deputies on the committee, Rajoy challenged them to present any evidence implicating his former minister.

Rajoy (left) has denied any knowledge of the alleged spying operation against his party's former treasurer Luis Barcenas
Rajoy (left) has denied any knowledge of the alleged spying operation against his party's former treasurer Luis Barcenas AFP / Pierre-Philippe MARCOU

The probe into the so-called "Operation Kitchen" spying affair is one of several opened after the arrest of ex-police chief Jose Manuel Villarejo, who for years secretly recorded conversations with top political and business figures in order to smear them.

"I don't know Mr Villarejo,..." Rajoy, who served as prime minister between 2011 and 2018, told the committee. "I have never spoken to him.

One conversation in the case files -- between Villarejo and the former treasurer Barcenas -- appeared to suggest that they had compromising material on Rajoy himself.

"I really don't care what Mr Barcenas and Mr Villarejo might have said about me," said Rajoy.

Both men had had serious problems in the courts, he pointed out, and so they defended themselves as they saw fit -- including lying.

Barcenas was at the heart of the so-called "Guertel" affair, which involved the illegal financing of the Popular Party.

After he was convicted in May 2018, Rajoy's government was brought down in a no-confidence vote a few days later.

Socialist Prime Minister Pedro Sanchez and his radical-left ally Podemos successfully pushed for the parliamentary investigation into the alleged spying operation inside the Popular Party.