A helicopter drops water to douse a fire on the Crimean bridge in Kerch on Saturday. AP

A blast on Saturday on the bridge over the Kerch Strait, a major supply route for Moscow's forces in southern Ukraine, prompted gleeful messages from Ukrainian officials but no claim of responsibility.

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"There is no doubt. This is an act of terrorism aimed at destroying critically important civilian infrastructure," Putin said on Sunday in a video on the Kremlin's Telegram channel.

"This was devised, carried out and ordered by the Ukrainian special services."

Security Council Deputy Chairman Dmitry Medvedev said ahead of Monday's meeting that Russia should kill the "terrorists" responsible for the attack.

Russian President Vladimir Putin attends a meeting.

"Russia can only respond to this crime by directly killing terrorists, as is the custom elsewhere in the world. This is what Russian citizens expect," he was quoted as saying by state news agency Tass.

The bridge is a vital artery for the port of Sevastopol, where the Russian Black Sea fleet is based, as well as an imposing symbol of Russia's 2014 annexation of the Crimean peninsula.

The damage to the bridge came amid battlefield defeats for Russia and initial reports from Ukrainian officials of a mass burial site discovered in the recently liberated eastern town of Lyman.

Putin's anger over the suspected attack also coincided with growing concerns that Moscow could resort to nuclear weapons, after Putin repeatedly cautioned the West that any attack on Russia could provoke a nuclear response.

Putin on Sunday met Alexander Bastrykin, the head of Russia's Investigative Committee, who presented findings of an inquiry into what he said was the explosion of a vehicle and subsequent fire on the bridge.

Reuters