Portuguese authorities searched the house of Spain's 2010 World Cup winning captain Iker Casillas on Wednesday as part of an ongoing investigation into alleged money laundering and tax fraud in the world of football.

Public prosecutors said authorities, including nearly 200 police officers, carried out 76 searches across the country at houses, football clubs, lawyers and agents' offices.

In a statement shared on Twitter, Casillas said he is "absolutely calm" with respect to the investigations and has "full confidence" in the Portuguese justice system.

Casillas wishes that "transparency reaches everyone and every corner of football," the statement read.

The operation, named Out of Play, is investigating alleged tax avoidance in the football business from 2015 onwards. According to the prosecutors, those involved allegedly dodged payments of tax owed to the Portuguese state.

Casillas, who led Spain to win Euro 2008 and 2012 as well as the 2010 World Cup, suffered a heart attack in May while training with current club Porto, and has not played since. He returned to training in November.

Portugal's biggest football clubs, including Porto, have already reacted to the investigation. Porto confirmed the club has been the target of searches and will collaborate with the investigation.

Last month, Casillas announced he would run for president of the Spanish Football Federation when elections are called later this year.