A Russian journalist known for his criticism of President Vladimir Putin has died after being beaten by unknown attackers, it has been reported.

Nikolai Andrushchenko, 73, who co-founded the Novy Peterburg newspaper, was attacked six weeks ago and had been in a coma since then.

He died on Wednesday in St Petersburg.

His attackers have not been identified but Novy Peterburg editor Denis Usov linked the assault to articles in the newspaper about corruption in the city.

Mr Andrushchenko was a member of the St Petersburg city council from 1990 until 1993. He made his name writing about human rights issues and crime.

In 2007 he was imprisoned on charges of defamation and obstruction of justice following his coverage of a murder investigation and trial in St Petersburg, according to the Committee to Protect Journalists (CPJ).

At the time Mr Andrushchenko's colleagues said they thought his detention was due to Novy Peterburg's critical coverage of local authorities ahead of parliamentary elections.

In November that year he was beaten by unidentified attackers, CPJ said.