The British government on Monday summoned the Russian ambassador to make clear its condemnation of what it described as the "politically motivated" conviction and sentencing of outspoken Kremlin critic Vladimir Kara-Murza, a British dual national.
Kara-Murza has spent years speaking out against President Vladimir Putin and lobbied Western governments to impose sanctions on Russia and individual Russians for purported human rights violations.
He was jailed for 25 years by a Moscow court on Monday after it found him guilty of treason and other offences he denied.
"Russia’s lack of commitment to protecting fundamental human rights, including freedom of expression, is alarming," British Foreign Secretary James Cleverly said in a statement.
"We continue to urge Russia to adhere to its international obligations including Vladimir Kara-Murza’s entitlement to proper healthcare."
Britain has already sanctioned the judge that presided over the trial for previous involvement in human rights violations, and said it would consider further measures to hold to account those involved in Kara-Murza's "detention and mistreatment".
(Reporting by Kylie MacLellan; editing by William James)