Since 2006 in the European Union we have to use the IBAN (an extension to the bank account number) for international payments.
Now a BLZ is part of the payment structure but that's only used in Germany and Austria. The BLZ is part of the IBAN.
From 2014 the IBAN is also needed for national payments so I think it's nessecary to add the IBAN (instead of the bank account number??) in the future.