SEOUL, South Korea -- North Korea says South Korea and the U.S. are behind a temporary Internet shut down this week. But an expert says it's too early to determine what happened.

The official Korean Central News Agency provided few details in its claim Friday of an attack.

Foreigners in Pyongyang reported no Internet access Wednesday and Thursday. The Bangkok-based company that operates North Korea's Internet confirms a cyberattack but says networks are normal Friday.

South Korea denies the allegation. The U.S. military declined to comment. A security expert says cyberattack investigations can take months, and that individual hackers are more likely to blame than governments in this case.

Only a small number of approved North Koreans can surf the World Wide Web.

Pyongyang also criticizes U.S.-South Korean military drills and new UN sanctions.