Russian police and security officers are among 10 suspects arrested over the murder of investigative journalist Anna Politkovskaya, Russian authorities say.
Anna Politkovskaya was killed as she left her apartment building
The prosecutor general said suspects included a security officer and a Chechen gang leader, and that evidence suggested a conspiracy planned abroad.
But a colleague of Politkovskaya said he was surprised by the statement.
The journalist, a vehement critic of President Vladimir Putin, was shot dead near her Moscow apartment last October.
Plotters 'beyond Russia'
"The individuals interested in eliminating Politkovskaya can only be ones living beyond Russia's borders," Prosecutor General Yuri Chaika told reporters.
"Above all, people and structures interested in destabilising the country, changing its constitutional order, in stoking a crisis in Russia... could gain from this crime," he said.
The chief prosecutor was shown briefing President Putin on the case
But Roman Shleynov, editor of the investigative unit at the liberal Novaya Gazeta newspaper where Politkovskaya worked, told the BBC it was too early in the investigation to be definite about suspects.
"There is no evidence of evil forces from abroad being involved," he said. "It reminds me of the practice in the Soviet Union when for every problem inside the country, top officials blamed usually somebody from the West."
He also questioned Mr Chaika's motives in making the remarks, saying political statements could influence the work of investigators on the ground.
The murder of Politkovskaya drew international condemnation, including allegations that President Putin was failing to safeguard freedom of speech.
Mr Chaika was shown on TV telling the president of the arrests, informing him that those held would soon be charged.
"The group was headed by a leader of a Moscow criminal group of Chechen origin," Mr Chaika said.
"Unfortunately, this group included retired and acting interior ministry and FSB (Federal Security Service) officers."
Mr Chaika said the same group may have been involved in two other high-profile murders: the 2004 killing of Paul Klebnikov, who edited the Russian version of Forbes magazine, and last year's killing of Andrei Kozlov, deputy head of the Russian central bank.
The arrested FSB officer was named as Lt Col Pavel Ryaguzov.
Mr Chaika said the Politkovskaya murder had been planned very carefully and had involved two groups keeping her under surveillance.
She was killed as she left for work. Closed circuit television footage showed a single gunman carried out the murder.
The Russian government has always strenuously denied any connection to the murder.
Politkovskaya made her name reporting from Chechnya for Novaya Gazeta.
She was also the author of two books in English, A Dirty War: A Russian Reporter in Chechnya (2001), and Putin's Russia (2004).
Her writing was often polemical, as bitter in its condemnation of the Russian army and the Russian government as it was fervent in support of human rights and the rule of law.