Russia on Monday detained a young woman after an explosion killed a top Russian military blogger and wounded dozens, claiming the bombing attack was orchestrated by Ukraine with the help of supporters of jailed Kremlin critic Alexei Navalny.

Ukraine has blamed Russia's domestic infighting for the blast in a Saint Petersburg cafe that on Sunday wounded more than 30 people and killed Vladlen Tatarsky, a high-profile supporter of Moscow's assault on Ukraine.

The attack came after Darya Dugina, the daughter of a prominent ultranationalist intellectual, was last August killed in a car bombing outside Moscow that Russia also blames on Ukraine.

Russia's Investigative Committee and the National Anti-terrorism Committee both said pro-Navalny activists were behind the latest attack.

The Investigative Committee released a video of the arrest of 26-year-old Darya Trepova, who it said "holds opposition views and is a supporter of the Anti-Corruption Foundation", referring to Navalny's banned organisation.

Political observers said the bombing attack could be used to justify a further crackdown on critics of Moscow's offensive in Ukraine.

Navalny's spokeswoman Kira Yarmysh said the attack could also be used to accuse the jailed opposition politician of new crimes.

"Alexei will soon be on trial for extremism," Yarmysh wrote, adding that he faced 35 years in prison.

"The Kremlin thought: 'It's great to be able to add the terrorism charge'."

The Kremlin condemned the "terrorist attack" and said "there is evidence... that the Ukrainian special services may be related to its organisation".

Ukrainian President Volodymyr Zelensky told journalists he was too busy focusing on his own country to pay attention to the attack in Saint Petersburg.

Tatarsky, whose real name is Maxim Fomin, was reportedly killed after receiving a statuette rigged with explosives during a talk at "Street Food Bar No. 1", located along the Neva River not far from the historic city centre.

The 40-year-old, who hailed from the eastern Ukrainian region of Donetsk, fought alongside pro-Kremlin separatists and then became a popular military blogger with half a million followers on social media.

At a Kremlin ceremony announcing the annexation of four Ukrainian regions last September Tatarsky recorded himself saying: "We will defeat everyone. We will kill everyone. We will rob everyone as necessary. Just as we like it."

- 'Heavy loss' -

 

President Vladimir Putin posthumously bestowed a top award, the Order of Courage, on Tatarsky citing his "courage and bravery shown during professional duty", said a Kremlin decree on Monday.

Russians placed flowers at a makeshift memorial in Saint Petersburg to honour the blogger, who served prison time before joining the pro-Kremlin separatists.

Igor Ivanov, an 18-year-old student, said he was shocked and added he closely followed Tatarsky. "This is a heavy loss," he said.

Vladislav Andreev, 27, compared Tatarsky's death to the bombing attack on Dugina.

"These people will stop at nothing," he said.

The footage released by the Investigative Committee showed a young blond woman getting in an elevator with a suitcase and then cut to her being led into a room by men dressed in dark uniforms.

The Russian interior ministry also published a video of Trepova in which she was heard saying she had brought a statuette that exploded to the Saint Petersburg cafe.

Asked on camera who gave it to her, the Russian national said she would answer "later".

"The terrorist attack was planned by Ukrainian security services with the help of agents working with the so-called Anti-Corruption Foundation," said Russia's National Anti-terrorism Committee.

- 'Blood and pieces of glass' -

 

At least 100 people reportedly attended the event when the bombing attack took place on Sunday.

Alisa Smotrova, who was at the cafe, told AFP:

"They put (the figurine) somewhere in the back without a second thought... and all of a sudden there was an explosion.

"There was blood and pieces of glass," she added.

The head of the Wagner paramilitary group, Yevgeny Prigozhin, said the venue used to belong to him.

Prigozhin said on social media that he "gave the cafe to patriotic movement Cyber Front Z and they organised various seminars there".

Cyber Front Z, which refers to itself on social media as "Russia's information troops", said it had hired out the venue for the evening.

Prigozhin said his forces hoisted the Russian flag with an inscription honouring the deceased blogger over the city administration of frontline hotspot of Bakhmut, which Wagner claimed to have seized.

On Sunday evening Ukrainian presidential aide Mykhaylo Podolyak suggested that the attack had taken place as a result of infighting in Russia.

"The question of when domestic terrorism would become an instrument of internal political fight was a matter of time," he said on Twitter.

The Russian foreign ministry on Sunday paid homage to the blogger and his "service to the Fatherland, which aroused Kyiv's hatred".