Car bombing in Moscow critically injures ex-adviser to former Ukraine PM, a day after deadly St Petersburg blast

A car bombing in Moscow has left a former adviser to Ukraine's ex-prime minister critically injured, one day after a military serviceman was killed in a similar attack in St Petersburg, according to Russian authorities.

Russia's Investigative Committee said the Friday explosion struck a vehicle driven by Sergei Zavorotnyi, who once served as an adviser to former Ukrainian Prime Minister Mykola Azarov. Zavorotnyi was taken to hospital with injuries, and the committee said it had opened a criminal case without naming any possible suspects.

The blast is the most recent in a string of bombings and shootings aimed at people connected to the war in Ukraine. Moscow has blamed Kyiv for the attacks, while Ukrainian authorities have not commented on either of this week's bombings.

Azarov led the Ukrainian government under President Viktor Yanukovych, the Moscow-friendly leader who was driven from power by protesters and fled to Russia in February 2014. Azarov also lives in Russia and told state-run television he was "shocked" by the attack on his former adviser, saying he believes Zavorotnyi was singled out because of his criticism of the Ukrainian government.

Zavorotnyi, 72, worked as a journalist for the Russian daily Komsomolskaya Pravda before joining Azarov's team. He went on to write a book about Yanukovych's removal from power and ran an online outlet that was critical of Ukrainian authorities. Russia's REN TV channel reported that he lost his left arm, sustained multiple other injuries and was in a coma following the explosion.

Al Jazeera's Yulia Shapovalova, reporting from Moscow, said an explosive device was believed to have been planted beneath the car and set off remotely while Zavorotnyi was driving. "The investigative committee has already launched a criminal case into this explosion," she said.

The previous day in St Petersburg, a military serviceman was killed when a bomb went off in his vehicle, the Investigative Committee said. Authorities did not identify the victim or indicate who might be responsible. The Fontanka news outlet reported the victim was a colonel, and other Russian online media described him as a senior air force officer, though Shapovalova said preliminary reports pointed to the victim being a military serviceman rather than a colonel in the Russian Air Force.

As in the Moscow attack, the St Petersburg victim was behind the wheel when the device detonated. "In both cases an explosive device was triggered remotely, and it was planted under their car," Shapovalova said. "Here in Russia, all the attacks are considered to be orchestrated by the Ukrainian side."