Russia's security service says it has detained four people it alleges were plotting terrorist bomb attacks in Moscow.
The Federal Security Service (FSB) said on December 15 that the detainees are citizens of Moldova and Tajikistan.
In a statement, the FSB said they were planning "a series of high-profile terrorist attacks in Moscow with the use of powerful improvised explosive devices."
It said they were acting on "direct instructions" from a member of the extemist group Islamic State (IS) who is based in Turkey and is wanted in Tajikistan for unspecified crimes.
The agency said it made the arrests in and around Moscow and found weapons and ammunition, as well as explosives.
Many people from Moldova and Tajikistan, two of the poorest former Soviet republics, come to Moscow and other Russian cities to look for work.
The FSB frequently announces that it has thwarted attack plots. Earlier this week, FSB Director Aleksandr Bortnikov said 42 terrorism-related crimes have been prevented in Russia this year.
The last major terrorist attack in Moscow was a suicide bombing in January 2011 that killed 37 people in the arrivals hall at Domodedovo International Airport.