The police on Monday intensified security outside the U.S. Embassy and other U.S.-related facilities here against possible terrorist attacks in retaliation for the U.S.-led attacks on targets within Afghanistan.

The police added one more armored car to 300 armed police dispatched around the U.S. Embassy near Kwanghwamun, central Seoul.

Police patrols of the embassies of U.S. allies, which have announced support for the U.S. retaliatory action against terrorism, were also intensified.

The U.S. Embassy is now closed in observance of the Columbus Day holiday but will operate normally starting Tuesday.

All together 21 police squads are guarding the official residence of the U.S. Ambassador and 67 other U.S. facilities nationwide.

Meanwhile, heightened security following the U.S. and British attacks on Afghanistan caused little traffic congestion in areas near the U.S. Army Base in Yongsan as it did after last month's terrorist attacks in the United States.

The United States and its allies are attacking Afghanistan's ruling Taliban and terrorist training camps within their territory, as they are Washington's prime suspects in the devastating kamikaze hijacking of four U.S. airliners used to destroy the World Trade Center and cripple the Pentagon.