Authorities have boosted security across Moscow after a suspected suicide bomber blew herself up outside a subway station, killing 10 people and wounding 51.
It was the second major terrorist attack in Russia in a week.
Police have increased patrols throughout the city, especially where crowds gather, including train stations and airports.
Witnesses say a woman approached the Moscow subway station Tuesday, but turned back when she saw police checking bags and blew herself up.
An Islamic extremist group calling itself the Islambouli Brigades has claimed responsibility for Tuesday's blast. It said on an Internet site that the bombing was in support of Muslim separatists in Chechnya.
The same group also took responsibility for last week's bombings of two Russian passenger jets, killing 90 people. Neither claim has been verified.
Information for this report is provided by AFP and Reuters.