The nation is on heightened alert towards possible terrorist attacks following a report that a member of the Al Qaeda was found to have secretly entered the country earlier this year.

A senior official of an intelligence organization said Tuesday that an Al Qaeda agent was confirmed to have boarded a plane bound for Seoul from Manila.

The intelligence official added that the agent apparently snuck into the country to investigate U.S. bases in South Korea and to make preparations for a terrorist crime on airplanes headed toward Northeast Asia.

The official said the alleged spy is currently on trial in the U.S. after being repatriated there earlier this year.