Moscow: In a major allegation amid the ongoing investigation into the Crocus City Hall attack, Russia's Federal Security Service (FSB) chief Alexander Bortnikov said on Tuesday that the United States, the United Kingdom and Ukraine are behind the terrorist attack, TASS reported.

"We believe that this is true. In any case, we are now talking about the factual information we have. This is general information, but they have a long record of this sort," he said after participating in an enlarged meeting of the Prosecutor General's Office board, when asked whether the US, Britain and Ukraine were behind the terrorist attack.

Bortnikov further said that Ukraine has been trying to prove it is 'capable enough'.

"What is it expected to do to demonstrate its capability? It is expected to carry out sabotage and terrorist acts in the rear. This is what both the chiefs of Ukraine's special services and the British special services are aiming at. US special services have repeatedly mentioned this, too," he said.

He pointed out that there was a large amount of information in the public space "showing that the West and Ukraine are out to cause greater harm to our country."

"There have been drone strikes, strikes by uncrewed boats at sea, and incursions by groups of saboteurs and terrorist organizations into our territory," Bortnikov concluded.

Notably, Russian President Vladimir Putin has repeatedly been pointing towards an alleged Ukrainian connection in the terror attack.

Earlier, Putin stressed that it needs to be answered who was waiting for the perpetrators of the attack on the Ukrainian side and why they headed exactly there.

"It is also necessary to answer the question - why the terrorists after committing the crime tried to head exactly to Ukraine, who was waiting for them there," he said. "It is clear that those who support the Kiev regime do not want to be accomplices of terror and sponsors of terrorism. But the questions are many, indeed."

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. The armed men opened fire and detonated explosives creating a massive euphoria and panic among the crowd.

The Islamic State (ISIS-K) had taken responsibility for the terror attack.

At least 139 people have been killed and 182 suffered injuries in the attack, according to TASS.

A total of 11 individuals suspected of being involved in the terrorist attack have been apprehended, including four gunmen who were detained in the Bryansk Region, southwest of Moscow, as they attempted to seek refuge by crossing the nearby Ukrainian border.

Russian 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 vowed to identify and punish all those who were behind the attack, TASS reported.

He also said that "radical Islamists" were responsible for last week's attack on a concert hall outside Moscow, but also suggested that Ukraine was also somehow involved, Al Jazeera reported.

"We know that the crime was committed by the hands of radical Islamists, whose ideology the Islamic world itself has been fighting for centuries," Putin said. "This atrocity may be just a link in a whole series of attempts by those who have been at war with our country since 2014 with the hands of the neo-Nazi Kyiv regime."

Meanwhile, the White House has repeatedly said that the terrorist attack at the concert hall in Moscow was carried out by ISIS at Crocus, and there is "no evidence" that the Ukrainian government had anything to do with this attack.

This was a terrorist attack that was conducted by ISIS. Mr. Putin understands that. He knows that very well. And look, there is absolutely no evidence that the government of Ukraine had anything to do with this attack," White House Press Secretary Karine Jean-Pierre said on Monday.

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