Airport operators have increased vigilance in response to multiple online threats of random attacks at airports.

Police are tracking down the writer of a post last Friday warning that they installed a bomb at Incheon International Airport and would hit people at the airport with a truck upon detonation before attacking them with a weapon.

According to Incheon International Airport Corporation(IIAC) and Korea Airports Corporation(KAC) on Monday, similar terror threats have been made against other airports in Gimpo, Gimhae, Daegu and Jeju.

A thorough search of the airports did not find any dangerous objects.

As of 12 a.m. Monday, the IIAC has raised its vigilance level from "attention" to "caution," increasing patrols and tightening employee identification at entries and exits, while the KAC has reinforced patrols and security at 14 airports under its jurisdiction since Sunday afternoon.