The Moscow metro bombings left 40 dead and dozens injured
Three alleged organisers of the March suicide bombings on the Moscow metro have been killed after resisting arrest, Russian officials say.
It was not immediately clear when or where the killings happened. All those involved in the bombings have now been identified, officials said.
Russian leaders previously warned that the masterminds of the attacks, which killed 40 people, would be "destroyed".
Two young women from Dagestan were identified as carrying out the attacks.
The 29 March bombings targeted two of the Moscow metro's commuter trains.
The three alleged planners died during "an attempt to detain three members of an illegal group", said the head of the Federal Security Service (FSB), Alexander Bortnikov.
"To our great regret, we were unable to detain them alive because they put up fierce armed resistance and were killed."
'Matter of honour'
Mr Bortnikov said the suspects included a man who had escorted the suicide bombers to Moscow and another who had accompanied one bomber to the station.
Russian President Dmitry Medvedev said there had been no option but to kill the "terrorists".
"Those who put up resistance have to be eliminated - you cannot show pity," the Russian leader was reported as saying at a meeting with Mr Bortnikov.
The FSB head said that efforts to find other identified planners of the attacks were continuing.
The suicide bombers were identified as a 17-year-old thought to be the widow of a Caucasus militants, and the 28-year-old wife of an Islamist rebel commander.
A Chechen militant leader, Doku Umarov, said he ordered the bombings.
Shortly after the attacks, Russian Prime Minister Vladimir Putin said that Russian investigators should view catching the organisers of the bombings as a "matter of honour".
He said the security services, who had been widely criticised in the media, should drag them "from the bottom of the sewers".