Police and South Korean officials were investigating the simultaneous shutdown Wednesday, March 20 of computer networks at several major broadcasters and banks. While the cause wasn't immediately clear, speculation centered on a possible North Korean cyberattack, AP said.

The shutdown came days after North Korea blamed South Korea and the United States for cyberattacks that temporarily shut down websites in Pyongyang.

Officials at the two South Korean public broadcasters KBS and MBC said that all computers at their companies shut down at 2 p.m. (0500 GMT). The officials said the shutdown was not immediately causing any damage to their daily TV broadcasts.

The officials declined to give their names saying they were not authorized to speak media.

YTN cable news channel reported the company's internal computer network was completely paralyzed. Local TV showed workers staring at blank computer screens, and at one coffee shop employees asked for cash, saying their credit card machine wasn't working.

The state-run Korea Information Security Agency confirmed that computers at at least five South Korean companies were down. The agency was investigating what caused the outage.

Shinhan Bank, a lender of South Korea's fourth-largest banking group, said the bank's system, including online banking and automated teller machines, has stopped working since 2:20 p.m. Thursday. The company is unable to conduct any banking activities at bank windows to customers including retail banking and corporate banking.