Head of Russia’s spy agency Federal Security Service (FSB), Alexander Bortnikov, has accused Ukraine of being behind the deadly attack on Moscow concert hall last week.

“We believe that radical Islamists prepared the action, while Western special services have assisted it and Ukrainian special services had a direct part in it,” Bortnikov said without giving details.

Some 139 people were killed when four armed men burst into the concert hall on Friday evening. Another 22 remain in a serious condition, including two children, officials say.

Bortnikov’s allegations followed similar comments made by Russian President Vladimir Putin who linked the attack to Ukraine despite acknowledging that ISIS affiliate groups were behind the attack. In his nationwide address following the attack, Putin said the four attackers who broke into the Crocus City concert hall in Moscow on Friday evening had planned to flee to Ukraine after the attack.

Ukrainian President Volodymyr Zelensky has condemned the Russian accusations: "Putin was talking to himself again... Again, he blames Ukraine. A sick and cynical creature."

Meanwhile Belarus President Alexander Lukashenko said on Tuesday that the suspects were headed for Ukraine because they feared tight controls on the Belarus border. Putin’s attempts to blame Ukraine for the terror attack in Moscow has been condemned by Western leaders.

The US has said Islamic State is "solely" to blame for the Moscow attack and France's Emmanuel Macron said it would be "both cynical and counterproductive" for Russia to try to exploit the situation to seek to turn it against Ukraine.