Britain on Wednesday imposed sanctions on six individuals in charge of the Arctic penal colony where Russian opposition leader Alexei Navalny died last week.
Western leaders have expressed outrage at the news from Russian authorities that Navalny, President Vladimir Putin's most prominent domestic critic, had fallen unconscious and died in prison on Friday.
Those sanctioned, including the head and five deputy heads of the penal colony, will be banned from the UK and have their assets frozen, British Foreign Secretary David Cameron said in a statement.
"It's 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 said.
"Those responsible for Navalny's brutal treatment should be under no illusion - we will hold them accountable."
Russia, which has denied involvement in the death of the 47-year-old former lawyer, said on Saturday that it was unacceptable for Britain to interfere in its internal affairs.
The European Union also moved closer this week to imposing new sanctions against Moscow over its war on Ukraine, as Navalny's widow Yulia Navalnaya said Putin must be held accountable.
Germany, Lithuania and Sweden were among EU countries calling for specific new penalties against Russia over Navalny's death.
The United States, too, will announce a major package of sanctions against Russia on Friday over Navalny's death and the two-year Ukraine war, President Joe Biden said on Tuesday.
Britain has imposed sanctions on more than 1,700 people and entities under its Russia sanctions regime since Russia's full-scale invasion of Ukraine in February 2022, the government said.
