MADRID: Spain's scandal-hit former king Juan Carlos I has submitted a declaration to the Spanish tax office seeking to put his financial situation in order, El Pais newspaper reported on Sunday.

The voluntary declaration was presented by his lawyer with sources telling the paper the move was in connection with an ongoing anti-graft investigation looking into his credit card use.

The legal probe was confirmed last month Spain's attorney general, with judicial sources telling AFP at the time they were looking at whether the former king used cards linked to accounts not registered in his name - which could constitute a possible money-laundering offence.

They said investigators were looking into funds deposited in at several Spanish bank accounts held by a Mexican business and a Spanish Air Force official, and whether they had been accessed by the former monarch.

Prosecutors had sent legal requests abroad to determine whether the monies deposited in the accounts had been hidden from the tax authorities. If proven, the allegations could constitute a money laundering offence for which he could be prosecuted given that the movement of funds and use of the credit cards occurred after his abdication in June 2014.

A spokesman for the Spanish tax office could not confirm or deny the El Pais report about the voluntary declaration, saying for legal reasons the agency could not comment on specific cases.