British Prime Minister David Cameron is "deeply concerned" about the 2009 jail death of lawyer Sergei Magnitsky and has raised the case with Foreign Minister Sergei Lavrov, he said in a letter made public Wednesday.

Sergei Magnitsky, a 37-year-old lawyer for Russia's one-time biggest equity fund, Hermitage Capital, died in November 2009 after nearly a year in Moscow jails.

Colleagues and human rights activists say he was denied adequate medical treatment and subjected to conditions that amounted to torture in a case that has sparked international condemnation and spooked investors.

Writing to Hermitage co-founder Bill Browder, who has led a campaign to prosecute those he considers responsible for Magnitsky's death, Cameron said he would continue to track the case ahead of a proposed visit to Russia later in the year.

"I have now been briefed about the case and am deeply concerned by its implications for the rule of law and respect for human rights in Russia," Cameron said in the letter released by Browder.

"I discussed the case with Russian Foreign Minister Sergei Lavrov when I met him … on Feb. 15," he added.

Cameron said he was particularly concerned about the lack of results from an official investigation into the case initiated by President Dmitry Medvedev.

Several prison officials were fired shortly after the death, although human rights campaigners at the Moscow Helsinki Group wanted a torture investigation.

The case has also triggered action in the U.S. Congress, where a bill has been introduced that would ban any Russian linked to Magnitsky's death from the United States.

Hermitage's investments in Russia turned sour when Browder was blocked from entering the country in 2005. He later claimed that Russian officials had embezzled $230 million of tax refunds.