Popular was taken over by Spain's largest bank Santander in early June for the symbolic price of one euro after European authorities stepped in to prevent its collapse.

Popular's rescue wiped out shareholders, including retail investors, and some of them have already begun filing lawsuits to determine who was responsible.

"This emphasises that there are contradicting versions in the comments made by different authorities of what has happened," Javier Cremades, lawyer of the Spanish Association of Minority Shareholders, told Reuters. He said there was a need for the judiciary to act in order to clear up the facts.

Spanish and European authorities said Spain's sixth biggest bank needed to be rescued because of its weak liquidity situation after a bank run.

During a parliamentary hearing in mid-June, Spain's Economy Minister Luis de Guindos said that Popular ran out of liquidity, and was not in a position to ask for more, because it lacked collateral.

But deputy governor of the Bank of Spain Javier Alonso said during a conference in Santander on Friday that the bank had had more collateral than was presented.

"But, given it didn't present it, we haven't seen it and thus I can't certify it," Alonso also said.

The Bank of Spain's deputy governor also acknowledged that it would have been very complicated for Popular to present the last lines of collateral.

"If you want to mobilise assets in other countries, you have to mobilise them in a way that is legally accessible to the Spanish central bank here (the provider of emergency liquidity), that is not a simple thing, it is not that easy," he said.

Asked by reporters if the Bank of Spain had not requested more collateral, he said: "How could you think that we didn't ask the lender?"

Alonso said Popular's response to a request for further capital was: "Maybe tonight." He also said that due to the run on the bank, any additional collateral might not have changed the outcome.

The deputy governor said it was Banco Popular itself that said it was not viable due to stressed liquidity.

Alonso did not want to establish a link between potential claims of shareholders and the liquidity situation of Banco Popular. He said that responsibilities would have to determined by legal authorities.