Ukrainian President Volodymyr Zelensky has strongly denied accusations by Russian President Vladimir Putin linking Ukraine to the Moscow concert hall attack by ISIS that killed 137 people.

The attack has exposed potential weaknesses in Russia's security measures and has led to criticism of Putin's focus on political dissent over national security.

Putin has been accused of using the tragedy to further political objectives by asserting Ukraine's involvement, despite U.S. intelligence confirming ISIS-K as the perpetrators.

Russian authorities have detained individuals allegedly trying to escape to Ukraine, fueling calls in Russia for more aggressive military action against Ukraine and the reinstatement of the death penalty.

As a result of the attack and the subsequent tensions, Russia has conducted military strikes on Ukraine's energy infrastructure, leaving over one million people without power.