North Korea is stealing ordinary South Korean citizens' identities to open Internet accounts and post messages denying Pyongyang's involvement in the recent sinking of a South Korean warship, Seoul's top spy agency said today.

Tensions are high on the divided Korean peninsula after the March 26 sinking of the Cheonan in the Yellow Sea off the west coast killing 46 sailors, one of South Korea's worst military disaster since the 1950-53 Korean War.

A torpedo fired from a North Korean submarine tore the ship in two, an international team of investigators recently concluded.

North Koreans have been registering with South Korean identification numbers to post material claiming the ship sinking as an event staged by Seoul, a National Intelligence Service official said today.

In South Korea, people need to provide their ID numbers when they open a Web account.

The posts called the sinking of the 1,200-ton patrol ship "a staged fabrication" and questioned the veracity of the multinational investigation findings, South Korea's Yonhap news agency reported, citing an unnamed government source.

These cyberattacks are an advanced form of North Korea's psychological warfare against the South, designed to cause social panic, distrust, and instability, according to Yonhap.