MOSCOW, March 25. /TASS/. Investigators have not yet arrived upon a final version of the causes of the terrorist attack on a crowded concert at the Crocus City Hall music venue in suburban Moscow late last week, including claims of the possible involvement of the terrorist group IS (Islamic State, outlawed in Russia), Russian Presidential Spokesman Dmitry Peskov said on Monday.

"The investigation is still underway and no specific scenarios have been announced as of yet," he told a news briefing. "Previous reports were preliminary and no official scenarios have been voiced as of yet."

"We need to wait for [confirmed] information from our official law enforcement bodies," Peskov added.

On the evening of March 22, a terrorist attack targeted the Crocus City Hall music venue in Krasnogorsk, Moscow Region, just over the Moscow city limits. According to the Russian Investigative Committee, the current death toll is 137, but may rise. The Moscow Region Health Ministry said that 182 people were injured.

Eleven individuals suspected of being involved in the terrorist attack have been apprehended, including four gunmen who were detained in the southern Bryansk Region as they attempted to seek refuge by crossing the nearby Ukrainian border.

President Vladimir Putin said in a televised address that, according to preliminary information, the Ukrainian side had prepared "a window" in the border especially for the terrorists to cross undetected. He promised to identify and punish all those who were behind the attack on Crocus City Hall and declared March 24 a day of national mourning for the victims.