Foreign fighters detained on Sunday in Russia's southern region of Dagestan were involved in financing a deadly attack on a concert hall near Moscow last month, the TASS news agency cited Russia's FSB state security service as saying on Monday.
The FSB also said that one of the four detained men had confessed to personally bringing weapons to the Moscow attackers, according to the Interfax news agency.
Russian authorities said on Sunday they had detained a group of men who were planning violent acts, but had provided no information on their nationality.
At least 144 people were killed in the March 22 attack. IS has claimed responsibility but Russia has also said it believes "Ukrainian nationalists" were linked to the attack, an assertion strongly denied by Kyiv.
The four men Russia has charged with carrying out the attack are ethnic Tajiks.
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