Russian authorities on Sunday arrested three people in the North Caucasus republic of Dagestan on charges of planning terrorist attacks, following a deadly attack on a concert hall near Moscow.
The arrests were made during an operation in Dagestan's capital Makhachkala and in the town of Kaspiysk, around 10 kilometres (six miles) to the south, the Russian National Anti-Terrorist Committee said in a statement.
"Three criminals planning to commit a series of terrorist crimes have been arrested," the statement added.
The announcement comes more than a week after an attack on the Crocus City Hall in Moscow's outskirts killed at least 144 people and injured 551.
The Islamic State group (IS) has claimed the attack, while Russian authorities insist Ukraine is responsible.
An anonymous security source quoted by the RIA Novosti news agency said two suspects were "trapped" in their flat in Kaspiysk before being apprehended.
"An automatic weapon and its ammunition, as well as a ready-to-use improvised explosive device, were found during the search of the scene of the arrests," the committee said, adding that the operation had not caused any casualties.
Twelve people were arrested following the concert hall attack, including the four alleged assailants, who were originally from Tajikistan, a former Soviet republic in Central Asia.
On Friday evening, the Russian security services also announced that they had arrested three "nationals of a Central Asian country" who were planning a bomb attack in southwestern Russia.