South Korean police today said they have strengthened security against possible terror attacks by North Korea, amid high tensions during this month's US-South Korean military exercises. In a statement, the National Police Agency said Police SWAT team and sniffer dogs are patrolling major subway stations and airports and security at other major public facilities has also been tightened. It said police commandos and armoured vehicles have been deployed to central Seoul to protect the US embassy. The statement said since the drills began on Monday, the South's police have conducted training against various forms of unconventional warfare and infiltration by enemy special forces. Pyongyang has labelled the regular Key Resolve/Foal Eagle drills, involving some 200,000 South Korean and 12,300 US troops, as an act of aggression and threatened retaliation.