MOSCOW  -- Four suspects detained Sunday in Russia's Dagestan Republic on terrorism charges were directly involved in the attack on the Crocus City Hall concert, the Russian Federal Security Service (FSB) said Monday.

The suspects provided money and weapons to the concert hall attackers, the FSB said in a statement, adding that they were also allegedly plotting a terrorist attack in a park in the city of Kaspiysk.

One of the suspects confirmed that he brought weapons from the city of Makhachkala and handed them to the concert hall attackers, according to footage published by the FSB.

The four suspects were detained in the cities of Makhachkala and Kaspiysk in Dagestan on Sunday during a special counter-terrorism operation.

Automatic weapons, ammunition and a ready-to-use improvised explosive device were found where the suspects were detained.