Some 50,000 cardholders are at risk Friday after a third-party credit card processor was hit by a security breach.

VISA and MasterCard have issued statements saying law enforcement officials are investigating whether card member data has been illegally accessed.

VISA issued an alert saying it "has received intelligence from a third-party entity indicating that a criminal group has plans to execute 'a large batch settlement fraud scheme,'" the Krebs On Security blog said.

Criminals have claimed to have access to account numbers and a merchant account in Eastern Europe, the alert said.

MasterCard and VISA reported their own systems have not been compromised, the Wall Street Journal said. 

The company will "continue to both monitor this event and take steps to safeguard account information," a MasterCard spokesman said in a statement.

VISA and MasterCard don't lend or issue cards to consumers; rather, they handle transactions for banks that issue their cards and those that handle transactions for merchants, the Journal said. 

VISA has more than 648 million U.S. credit, debit and prepaid cards and MasterCard has more than 30 million U.S. credit, debit and prepaid cards in the market, according to the Nilson Report, a payments-industry newsletter.