Spanish tax authorities carried out new searches of former IMF chief Rodrigo Rato's Madrid offices in a money-laundering probe as the country questioned whether he had been made a scapegoat in the ruling Popular Party's anti-corruption drive.

Rato is already being investigated for alleged fraud during his time as chief executive at Bankia, a Spanish bank which needed to be bailed out by the government.

The 66-year-old told El Pais newspaper that he was "actively cooperating with investigators" in the new investigation.

Spain's state prosecutor ordered the searches as part of a probe into suspected money laundering, fraud and asset-stripping, a source close to the investigation told AFP.

The judge in charge of the investigation also ordered Rato's bank accounts be frozen Friday, a judicial source said.

Spanish media reported the investigation could be linked to an alleged payment of 6.2 million euros ($6.6 million) which investment bank Lazard made to Rato in 2011, several years after he worked for the bank as an adviser.

On Thursday, police escorted Rato out of his apartment building in an upscale neighbourhood in central Madrid after searching his flat for nearly four hours. His offices were also searched.

Rato, who headed the IMF between 2004 and 2007, is a former senior member of Spain's conservative Popular Party (PP) and also served as finance minister in prime minister Jose Maria Aznar's government.

Many in Spain were asking Friday whether Rato was being singled out by current Prime Minister Mariano Rajoy, who has been criticised for failing to crack down on corruption.

Opinion polls show the PP is losing support ahead of regional elections on May 24, with general elections looming before the end of the year.

Political analyst Anton Losada said: "The PP has noticed that corruption is causing it more trouble than it thought... and in Rato it sees an unmissable opportunity.

"He has already been burned and they have decided to make an example of him."

Rato has already been questioned on suspicion of fraud in an ongoing probe into the stock market launch of Bankia.

He is suspected of misrepresenting Bankia's accounts ahead of its doomed stock market listing and has been charged with fraud, embezzlement and forgery.

Rato has also been questioned in court as part of another probe into alleged spending sprees on company credit cards by him and other ex-managers of Bankia. He has denied wrongdoing in both cases.

Bankia nearly collapsed in 2012 and had to be bailed out by the Spanish government to the tune of 24 billion euros.

Spain later received 41 billion euros from international creditors to protect its entire banking sector from collapse, though it avoided having to seek a full sovereign bailout like Greece.

Thousands of customers have brought separate lawsuits against the Bankia group, saying they lost their money after being misled into converting their savings into the bank's shares.