SEOUL, South Korea - Some computer systems in South Korean remain down after a cyberattack caused networks at major South Korean banks and top TV broadcasters to crash simultaneously Wednesday.

Police and South Korean officials couldn't immediately determine responsibility, but some experts are pointing to North Korea. While North Korea's state media made no immediate comments on the shutdown, the rivals have been exchanging threats amid joint U.S.-South Korean military drills and in the wake of U.N. sanctions meant to punish North Korea over its nuclear test last month.

The cyberattack caused screens to go blank at 2 p.m. local time and more than seven hours later some systems were still down. It paralyzed bank machines across the country and froze part of the country's commerce, with customers unable to use the debit and credit cards that many rely on more than cash.

However, the disruption did not affect government agencies or potential targets such as power plants or transportation systems.

The network paralysis follows North Korean accusations that South Korea and the U.S. were behind a cyberattack that shut down its websites for two days last week.