Russian President Dmitry Medvedev has ordered an investigation into the circumstances surrounding the death of a lawyer in prison.

The lawyer, 37-year-old Sergei Magnitsky, was working for an investment company under investigation for tax evasion.

Mr Magnitsky was jailed last year and died earlier this month in the prison sick bay. The cause of death was recorded as heart failure. Critics say he was maltreated and received insufficient medical attention.