As Russia grapples with one of its worst terror attacks in history, the ruling establishment has been suspiciously eying Ukraine's involvement.
In a statement issued separately by Russia's FSB security service and Dmitry Medvedev, the deputy chairman of the Security Council of Russia, both have insinuated Kyiv's involvement in the attack. While FSB claimed that the assailants of the Moscow concert hall terror attack had contacts in Ukraine and were trying to flee there, Medvedev vowed to retaliate strongly if Ukraine's involvement is discovered.
"After committing the terrorist attack, the criminals intended to cross the Russian-Ukrainian border, and had appropriate contacts on the Ukrainian side," the state-run TASS news agency quoted the FSB as saying, after it announced 11 arrests over the attack.
"Terrorists understand only retaliatory terror," Medvedev said according to according to Russian-state media TASS News.
"No courts will help if force is not countered by force, and deaths by total executions of terrorists and repressions against their families," he said.
"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."
The Ukrainian foreign ministry strongly, however, firmly rejected these claims saying that these are planned provocations to further fuel anti-Ukrainian hysteria in Russian society.
Ukraine said it viewed any such allegation "to be a planned provocation by the Kremlin to further fuel anti-Ukrainian hysteria in Russian society, create conditions for increased mobilisation of Russian citizens to participate in the criminal aggression against our country and discredit Ukraine in the eyes of the international community".
Meanwhile, Russia has arrested 11 people -- including all four assailants -- over Friday's deadly attack on a concert hall, Russian news agencies reported on Saturday.
The head of the FSB security service informed Russian President Vladimir Putin "about the detention of 11 people, including all four terrorists directly involved in carrying out the attack," Russian state news agencies cited the Kremlin as saying in a statement.