Russian investigators have detained ten people in connection with the killing of Anna Politkovskaya, the crusading journalist, including former and serving members of Federal Security Service and the Interior Ministry, Russia's prosecutor general said on Monday.

But Yuri Chaika also told reporters that investigators were convinced that the person who ordered the killing of Ms Politkovskaya, who was gunned down outside her apartment building last October, was outside the country and plotting to destabilise President Vladimir Putin's government.

"We reached the conclusion that the only people who could be interested in the removal of A. Politkovskaya are those outside the territory of the Russian Federation," Mr Chaika told a press conference. "This is most of all to the advantage of those people and structures aiming at destabilizing the situation in the country, in changing the constitutional order, in creating a crisis in Russia and in a return to the previous system when everything was decided by the money of the oligarchs," he said.

He added that former and serving employees of the Interior Ministry and the FSB - the successor agency of the KGB - had "unfortunately" taken part in tracking Ms Politkovskaya's movements before her death.

Some observers have speculated that past and present members of the security forces have been involved in a series of killings whose victims have included critics of the Kremlin. This is the first time such officials have been cited by prosecutors in connection with one of these cases. Her killing, on the same day as Mr Putin's birthday, sparked outrage among Russian journalists and opposition figures.

Mr Chaika's comments came just one day after fierce Kremlin critic and oligarch-in-exile Boris Berezovsky, who is wanted by Russian prosecutors in a fraud case, again called for the overthrow of President Vladimir Putin's regime in an opinion piece in the Sunday Times, his third such public call.

In the immediate aftermath of Politkovskaya's killing, Mr Putin hinted he believed unnamed fugitives from Russian justice were behind the crime, claiming her death was much more damaging to Russia than any of her reporting.

Mr Chaika said he was not yet in a position to name the organisers or the perpetrators of the killing. But he said prosecutors believed a Chechen leader of a Moscow organised crime group was behind Ms Politkovskaya's killing.

He told reporters that investigators believed the "group" behind Ms Politkovskaya's killing was also involved in the murders of deputy central banker Andrei Kozlov, who was gunned down outside a football stadium last September, and of Paul Khlebnikov, the US editor of Forbes magazine in Russia , shot dead outside his office in July 2004.

Journalists at Novaya Gazeta, the independent newspaper renowned for its investigative journalism where Ms Politkovskaya worked, had warned in a statement on the newspaper's website that the real organizer of the killing could never be indicted as the case was used to fit "pre-election political intrigues."

Ms Politkovskaya had made a name as a fearless chronicler of human rights abuses by the military in Chechnya and as an outspoken critic of Russian president Vladimir Putin's clampdown on democratic freedoms. Her name had been included on several lists of so-called enemies of the Russian people on ultranationalist web sites.