As part of a thorough reform, the IOR is tightening controls on account-holders.
The IOR will only hold accounts for Catholic institutions and religious orders, clerics, employees and former employees of the Vatican, and diplomats accredited to the Holy See.
The bank is now closing the accounts of all clients who do not fall into one of those categories.
The IOR has been working steadily to counter complaints that the bank had been vulnerable to money-laundering.
But in closing accounts, IOR officials said that they did not mean to suggest that the account-holders were under suspicion.
Rather, the bank is pursuing a series of reforms intended to ensure that the institution is focused on the original purpose for which it was founded, to provide support for religious works, rather than to function as an ordinary bank.