Russia's top security agency said Monday it has broken up what it called a "terrorist cell" in southern Russia whose members had provided weapons and cash to suspected attackers of the Moscow concert hall.

The Federal Security Service, or FSB, said that on Sunday it detained four suspected members of the cell in the Russian province of Dagestan in the North Caucasus.

The agency alleged that the suspects detained in Dagestan were involved in channeling funds and providing weapons to the gunmen who attacked the concert hall on Moscow's western edge on March 22, killing 144 people in the deadliest attack on Russian soil in two decades.

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"The detained militants directly participated in financing the perpetrators of the March 22 terror attack on the Crocus City Hall in Moscow and providing them with terror means," the FSB said in a statement.

It said one of the suspects detained in Dagestan had confessed to personally bringing weapons to the Moscow attackers.

The FSB released a video showing one of the suspects saying that they also planned an attack in the city of Kaspiysk in Dagestan. It wasn’t clear whether the two confessions came from the same person.

The agency said the suspects are foreign nationals, without specifying their nationality. The suspected attackers of the Moscow concert hall arrested hours after the March 22 raid are citizens of the Central Asian nation of Tajikistan.

The detention of four suspects in Dagestan follows the arrest of the four suspected gunmen and seven others who were accused of involvement in the attack.

An affiliate of the Islamic State group claimed responsibility for the attack. President Vladimir Putin acknowledged that "radical Islamists" conducted the raid, but alleged - without providing evidence - that Ukraine and the West were involved, despite Kyiv's vehement denials.