The pledge came a day after Central Bank governor Ali Allaq appeared in front of lawmakers to answer questions on a range of issues, including the case which dates back five years.

"At the end of 2013, the vaults of the Rafidain Bank were flooded because of huge rains at the time, damaging the bills that were stored there," he said.

"They were worth around seven billion dinars," or six million dollars, said Allaq, who was not governor at the time.

He said the Central Bank reprinted new bills to replace the soaked ones but, since the money had not been in circulation, the only real "loss" was the cost of printing.

His comments, made during a six-hour parliament session, apparently did little to reassure Iraqi lawmakers.

"The bank governor said the (damaged) bills were destroyed, but that answer isn't clear," said MP Hoshyar Abdallah of Kurdish anti-corruption party Goran and a member of parliament's finance committee.

"We have concerns over how water entered the vault -- this is a source of suspicion for us. That's why we will conduct an investigation into this as soon as possible," Abdallah told AFP on Tuesday.

The issue has sparked controversy in Iraq -- ranked by Transparency International as the 12th most corrupt country in the world.

Corruption, shell companies and "phantom" public employees who receive salaries but do not work have cost Iraq the equivalent of $228 billion dollars since 2003, according to Iraq's parliament.

That figure is more than the country's gross domestic product and nearly three times the annual budget.