Russian President Vladimir Putin expressed deep condolences following Friday’s attack at a concert venue near Moscow, calling it a “barbaric terrorist act” in a video statement released Saturday.

He said the perpetrators “tried to hide and moved towards Ukraine, where, according to preliminary data, a window was prepared for them on the Ukrainian side to cross the border.”

Several Ukrainian agencies have categorically denied any connection with the attack, and the Russian officials who have alleged Ukrainian involvement haven’t offered any evidence.

Putin declared Sunday a day of mourning for the victims of the attack and described it as a bloody and barbaric act, which killed dozens of peaceful, innocent people. He expressed gratitude to emergency service workers who “did everything to save people’s lives, to get them out from under fire, from the epicenter of fire and smoke,” and to avoid even greater losses.

He promised the government would provide the necessary assistance to everyone, and added that additional anti-terrorist and anti-sabotage measures are being introduced in Moscow and the Moscow region.

-CNN