'Death for death': Russia accuses Ukraine, promises revenge for Moscow attack

"Death for death," Deputy Chairman of the Security Council of the Russian Federation Dmitry Medvedev said of Friday's terror attack, for which ISIS has claimed responsibility, while implying that Russia would retaliate if Ukraine had been involved, according to Russian-state media TASS News.

Ukraine denies any involvement in the attack, for which ISIS has claimed responsibility, and which US National Security Council spokesperson Adrienne Watson said on Saturday that "ISIS bears sole responsibility for." 

Speaking about supposed Ukrainian involvement, Medvedev said, "Terrorists understand only retaliatory terror," suggesting the death penalty for perpetrators, adding, "if it is established that these are terrorists of the Kyiv regime, it is impossible to do otherwise. All of them must be found and mercilessly destroyed as terrorists, including officials of the state that committed such an atrocity."

Russian Foreign Ministry spokeswoman Maria Zakharova said on Friday that a statement about a shooting near Moscow from the office of the UN Secretary-General had been too weak.

She said the statement, which spoke of being saddened by the violence, was insufficient.

Ukraine denies involvement, US says ISIS is solely responsible

Ukrainian presidential adviser Mykhailo Podolyak said on Friday that Kyiv had nothing to do with Friday's attack by gunmen at a Moscow concert hall.

"Let's be straight about this: Ukraine had absolutely nothing to do with these events," Podolyak said in a video message posted on Telegram.

"We have a full-scale, all-out war with the Russian regular army and with the Russian Federation as a country. And regardless of everything, everything will be decided on the battlefield," Podolyak said.

US National Security Council spokesperson Adrienne Watson said on Saturday that there "was no Ukrainian involvement whatsoever" in the attack, adding that the US government early this month shared information with Russia about a planned attack in Moscow and also issued a public advisory to Americans in Russia on March 7.