Politkovskaya's reports exposed alleged abuses of power by officials

Ms Politkovskaya was shot dead near her flat in Moscow in 2006.

She won fame by exposing atrocities against Chechen civilians by Russian-backed security forces.

Last month, a former Chechen politician was charged with being an accomplice in the murder. Ten suspects were arrested in August, two of whom were then freed.

Russia's Interfax news agency quoted a source close to the investigation as saying Lt Col Pavel Ryaguzov from the Federal Security Service was among those charged.

Investigators believe that he could have passed on details of Ms Politkovskaya's address to another suspect, who in turn gave them to the killer, the source said.

Kremlin 'interference'

Chief prosecutor Yuri Chaika said at the time that among the suspects were serving and former security officers and that their ringleader was a Chechen gang boss.

At least two suspects have since been released.

Mr Chaika said there were indications that the murder plot had been masterminded abroad with a view to discrediting the Kremlin.

Ms Politkovskaya was a strong critic of President Vladimir Putin - especially his military campaign in Chechnya.

Her former colleagues at Moscow newspaper Novaya Gazeta accused Kremlin hardliners of interfering in the murder investigation after a lead prosecutor in the case was replaced in September.