Spanish bank Santander said Tuesday that some of its customer data in Spain, Chile and Uruguay, as well as that of its current and former employees, had been subject to unauthorized access in a database hosted by an external provider.

The euro zone's second-largest bank by market value said in a statement that it "immediately implemented measures to manage the incident," including blocking compromised access to the database.

Without giving further details about the breach, Santander said it had also put in place additional fraud prevention controls to protect affected customers.

Its banking operations and systems were not affected, Santander said, adding that customers could continue to transact safely and that no transaction data, or credentials to enable transactions, were stored in the database.

Customer data in all other markets and businesses was not affected.

The bank has informed regulators and law enforcement and will continue to work closely with them, while proactively and directly contacting those affected.

(Reporting by Inti Landauro and Jesús Aguado; editing by Andrei Khalip; Spanish edition by Mireia Merino and Benjamín Mejías Valencia)