Russia on Monday threatened to retaliate after Britain sanctioned a number of Russian officials for their alleged involvement in the death of lawyer Sergei Magnitsky.
"The Russian side reserves the right to take retaliatory measures in connection with Britain's hostile decision," the Russian embassy in London said in a statement without elaborating.
The mission said Moscow was particularly outraged by the sanctioning of top directors of Russia's Investigative Committee and General Prosecutor's Office as well as judges.
"In Russia, investigators, prosecutors and judges carry out their responsibilities independently of executive authorities and are guided by law alone," the embassy said.
Under its first post-Brexit targeting of accused human rights violators the UK sanctioned 25 Russian officials including Alexander Bastrykin, the head of the powerful Investigative Committee which reports directly to President Vladimir Putin.
Magnitsky, a tax consultant for British financier William Browder, died in prison of untreated illness in 2009 after accusing Russian officials of $230 million tax fraud.
Russia has rejected the claims and convicted Magnitsky of fraud, putting him on trial posthumously.
Browder has vowed to avenge his death, pushing the West to adopt legislation punishing Russian officials for rights violations.
Writing on Twitter, Browder thanked UK Foreign Secretary Dominic Raab for announcing the sanctions, calling them a "huge milestone."
Britain also sanctioned a number of individuals from Saudi Arabia and North Korea.
London has accused Russia of "destabilising" activities including the 2018 chemical attack that almost killed former spy Sergei Skripal and his daughter.
Russia has rejected accusations that officers from its GRU military intelligence agency used a powerful nerve agent to poison Skripal in retribution for his work with British and other Western spy services.
