The UK has frozen the assets of six Russian prison bosses in charge of the Arctic penal colony where opposition leader Alexei Navalny died.
The sanctioned individuals will also be banned from travelling to the UK.
Western leaders say the blame for Navalny’s death lies with the Russian authorities, including President Putin.
“Those responsible for Navalny’s brutal treatment should be under no illusion – we will hold them accountable,” UK Foreign Secretary Lord Cameron said.
The UK is the first country to impose sanctions in response to his death, the Foreign Office says.
The US has also announced it will be unveiling its own package of sanctions against Russia over Navalny’s death and the ongoing war in Ukraine on Friday.
The British government has called for Navalny’s body to be released to his family immediately and for a full and transparent investigation to take place.
The appeal from the UK echoes similar calls from Navalny’s mother, who was filmed on Tuesday outside the colony where he died saying she had been trying to see him for five days but did not even know where he was.
Those sanctioned by the UK are; Col Vadim Konstantinovich Kalinin – head of the penal colony, Lt Col Sergey Nikolaevich Korzhov – deputy head, Lt Col Vasily Alexandrovich Vydrin – deputy head, Lt Col Vladimir Ivanovich Pilipchik – deputy head, Lt Col Aleksandr Vladimirovich Golyakov – deputy head and Col Aleksandr Valerievich Obraztsov – deputy head
Announcing the sanctions, Lord Cameron said it was “clear that the Russian authorities saw Navalny as a threat, and they tried repeatedly to silence him”.
“No-one should doubt the oppressive nature of the Russian system,” he added. “That’s why we’re today sanctioning the most senior prison officials responsible for his custody in the penal colony where he spent his final months.
“Those responsible for Navalny’s brutal treatment should be under no illusion – we will hold them accountable.” Meanwhile, Prime Minister Rishi Sunak said the UK and its allies were considering “all options to hold Russia and Putin to account”.
Labour leader Sir Keir Starmer said Navalny’s death was a “reminder that Putin has stolen not just the wealth but also the future and democracy of the Russian people”.
Conservative MP Alicia Kearns, who chairs the Foreign Affairs Committee said UK measures against Russia needed to “go a lot further”.
Navalny, who was the Russian opposition’s most significant leader for the last decade, had been serving a 19-year sentence on charges many viewed as politically motivated.
The Russian prison service said he died at the IK-3 Arctic penal colony on Friday after taking a walk and suddenly collapsing. Navalny’s team alleges he was murdered on the orders of President Putin.
The family have been told his body will not be released for two weeks. His mother was informed it was being held for “chemical analysis”, a representative for Navalny said.
There has been no confirmation of the whereabouts of the body from Russian authorities, while efforts to locate it have been repeatedly shut down.
Navalny’s wife, Yulia Navalnaya, has alleged the body was being kept until traces of poisoning by the nerve agent Novichok had disappeared. Navalny survived an attempt to kill him using the poison in 2020.
Mr Putin has not directly commented on his death. The Kremlin did acknowledge his death and said the Russian president was aware.
