The British government has imposed sanctions on six individuals in charge of the Arctic penal colony where Russian opposition leader Alexei Navalny died last week.

The Foreign Office announced on Wednesday that the officials will be banned from Britain and their assets will be frozen.

The Foreign Office said Navalny was denied medical treatment and had to walk in temperatures of minus 32 degrees Celsius while being held in the prison.

Foreign Secretary David Cameron said, "It's clear that the Russian authorities saw Navalny as a threat and they tried repeatedly to silence him." He added, "No-one should doubt the oppressive nature of the Russian system."

The Foreign Office said Britain is calling on Russian authorities to immediately release Navalny's body to his family following reports that they have been denied access to it.