North Korea appears to have been informed of the deployment of a nuclear-powered U.S. aircraft carrier to the South, through an internet posting a local firm registered to hire temporary drivers to transport U.S. sailors, the Defense Ministry said Tuesday.

On Sunday, Pyongyang berated Washington for deploying the 97,000-ton USS Nimitz aircraft carrier around Friday shortly after the end of the allied military exercise, which it criticized as a rehearsal of a nuclear war of incursion.

The North’s statement surprised Seoul officials as they did not officially announce the deployment of the carrier. Some argued that some operational military secrets might have been leaked to the communist state.

Seoul’s Defense Ministry launched an inquiry to find out how the North got the information and found a set of online postings looking for temporary drivers who can transport the U.S. sailors when they arrive at a port in Busan from May 11 through 13.

The aircraft carrier left a port in San Diego on April 19 and entered the operational area for the U.S. Seventh Fleet based in Yokosuka Japan last Friday. It is expected to join an allied maritime exercise in the East and South Seas at the end of the ongoing drills taking place in the West Sea.

By Song Sang-ho (sshluck@heraldcorp.com)