Investigators said Ukraine was behind a car explosion on Saturday that killed one person and wounded pro-Kremlin writer Zakhar Prilepin, one of Russia's best-known novelists.
Investigators said they were "probing Alexander Permyakov's involvement in the assassination attempt on Zakhar Prilepin".
"During the interrogation [the suspect] testified that he acted on the instructions from the Ukrainian special services," said Russia's investigative committee, which looks into major crimes.
Ukrainian presidential aide Mykhaylo Podolyak reacted by likening Putin's regime to a god that "devours his enemies ... and ultimately devours his own," implying the blast was due to Russian infighting.
This is the latest in a series of apparent attacks and sabotage operations that Russia has blamed on Ukraine, ahead of the popular May 9 celebrations of the Soviet victory over the Nazis.
No one has claimed responsibility for most of the alleged attacks but the Kremlin has generally blamed Ukraine or the West, rarely providing evidence.
Saturday's blast took place at around 11:00 am in Russia's Nizhny Novgorod region, where nationalist writer Prilepin is from, some 400 kilometers east of Moscow.
The investigative committee published images of a partly destroyed, overturned car and said the writer had been taken to a medical facility.
A video released by the interior ministry earlier showed the suspect in handcuffs, wearing a khaki cap and a black hoodie.
Prilepin is known for novels drawing on his experiences of serving with Russian forces in Chechnya and as a member of a banned radical nationalist group.
The shaven-headed writer has been a frequent visitor to pro-Russian separatists in eastern Ukraine since the start of the conflict in April 2014.
After the start of the full-scale offensive in 2022, he was in a group of pro-Kremlin figures that launched what they dubbed a fight against the "anti-state position" of Russia's cultural elite.
They demanded the resignation of some cultural figures over what they said were unpatriotic positions.
There have already been two high-profile killings of Russian nationalists blamed by Moscow on Ukraine.
In April, a blast from a statuette rigged with explosives killed 40-year-old pro-Kremlin military blogger Vladlen Tatarsky, an attack the Kremlin said had been orchestrated by Ukraine with the help of supporters of jailed Kremlin critic Alexei Navalny.
In August, Darya Dugina, the daughter of a prominent ultranationalist intellectual, was killed in a car bombing outside Moscow, which Russia blamed on Ukraine. Kyiv denied the charges.
