MOSCOW, March 26 (Xinhua) -- The terrorist attack at the Crocus City Hall concert venue was prepared by radical Islamists, and the Ukrainian intelligence services were directly involved, said Director of Russia's Federal Security Service (FSB) Alexander Bortnikov.

"We believe that the attack was prepared by radical Islamists, and naturally Western intelligence services also contributed to this," Bortnikov said in an interview with TV broadcast Rossiya 1, adding that Ukrainian special services were "directly involved."

The Western intelligence and Ukraine needed the Crocus City Hall terrorist attack to create panic in Russian society, he noted.

Previously, Ukrainian authorities have repeatedly rejected claims of Ukraine's involvement in the attack.

A shooting occurred Friday in the Crocus City Hall concert venue in suburban Moscow, followed by a massive fire. The Russian Investigative Committee said that at least 139 people were killed as a result of the terrorist attack.