(Reuters) - Russia maintained extra patrols around the Moscow metro, military and key energy sites on Thursday, following a warning from the country's spy chief two days earlier of a potential attack by extremists.
Spy chief Nikolai Patrushev, who also heads the state's anti-terror committee, triggered the alert on Tuesday when he said foreign allies had passed on information pointing to a possible strike.
The warning was the first alert from the anti-terror committee, set up last year to coordinate Russia's response to threats of attacks, reports Trend.
"We continue to carry out the same measures we did yesterday, on transport and the metro," Nikolai Sentsov, the committee's spokesman, said.
On Wednesday the committee said no evidence had been found to support information about an attack but it pledged to continue heightened security for the time being.
Russia's three biggest mobile phone operators also switched back on transmitters on Thursday in the Moscow metro which the authorities had ordered be turned off a day earlier over fears of a possible remote control bomb.
Authorities have not specified where any potential threat may come from but Chechen separatists have fought two wars against Russia since 1994.
In the last few years Chechen groups have attacked Moscow's metro and concert venues and taken hundreds of prisoners in a theater siege in the center of Russia's capital and at a school in Beslan, in the southern Russian republic of North Ossetia.
Islamic fundamentalists have taken root in Chechnya's neighboring republics of Dagestan and Ingushetia and have contact with similar radicals in Afghanistan and Iraq.
Russia does not have a national alert scale, though Sentsov said one would be considered.