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

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.

The company does not know what caused the paralysis.

Immediate suspicion fell on North Korea.

Tensions between the neighboring countries are high following North Korea's recent nuclear test and U.N. sanctions that followed. Accusations of cyberattacks on the Korean Peninsula are not new. Seoul believes Pyongyang was behind at least two cyberattacks on local companies in 2011 and 2012.

Internet access in Pyongyang was intermittent at times last week, and Loxley Pacific Co., the broadband Internet provider for North Korea, said it was investigating an online attack that took down Pyongyang servers. A spokesman for the Bangkok-based company said Friday that it was not clear where the attack originated. Experts indicated it could take months to determine what happened and one analyst suggested hackers in China were a more likely culprit.

North Korea's official Korean Central News Agency blamed the shutdown on the United States and South Korea, accusing the allies of expanding an aggressive stance against Pyongyang into cyberspace with "intensive and persistent virus attacks."

South Korea denied the allegation and the U.S. military declined to comment.