MOSCOW, January 19 (RIA Novosti) - Russian security and police units stood down and resumed routine operations Friday after warnings from an unnamed foreign intelligence service of possible terrorist attacks on the country's public transportation system proved unsubstantiated.

Federal Security Service (FSB) director and head of the National Anti-Terrorism Committee Nikolai Patrushev announced the heightened alert January 16.

The national security service, which did not specify which country issued the warnings, recommended that heads of passenger transport companies take pains to ensure people's security and advised passengers to inform police of anything suspicious.

Anti-terrorism policing was stepped up in the Moscow metro, and the FSB's regional departments throughout Russia were put on high alert to forestall any attacks.

Security was also reinforced at especially important military and state facilities, natural gas and oil companies. Organized trips of schoolchildren on public transport were canceled until further notice.

The Anti-Terrorism Committee said over 500 suspicious items had been scrutinized in public places and more than 60,000 identity checks carried out, with five people on a wanted list arrested.

Police received and verified some 150 phone calls reporting suspicious facts. The enhanced security measures helped seize 10 kilograms of explosives in the Urals.

Two bomb explosions in Moscow's metro system in 2004 killed a total of 49 people and injured more than 300.

A bomb detonated in a train carriage between the central metro stations Avtozavodskaya and Paveletskaya in February, and in August another went off near the entrance to Rizhskaya station in northern Moscow.