A 10th person suspected of involvement in an attack on the St Petersburg metro earlier this month has been detained, Russian security officials say.
Akram Azimov is said to be the older brother of Abror Azimov, the suspected planner who was arrested on Monday.
The older Azimov is believed to have transferred funds used for the attack and set up links with international terrorist organisations.
The bombing killed 14 and injured more than 50 people.
Suicide bomber Akbarzhon Jalilov also died in the blast.
Both Azimov brothers are naturalised Russian citizens from Kyrgyzstan.
The Federal Security Service (FSB) said in a statement that Akram Azimov, born in 1988, was detained in a village outside Moscow on Wednesday.
Video footage of the arrest released by the FSB and shown on the Tass news agency website appeared to show a grenade in his money belt.
The statement described him as the “older brother of the presumed organiser” Abror Azimov.
Officials previously said they believed Abror Azimov had trained Jalilov, a Kyrgyz-born Russian, ahead of the bombing.
However, speaking in a Moscow court on Tuesday, Mr Azimov said he “was involved, but not directly”.
He denied reports by his lawyer that he had confessed to organising the attack.
The other eight people detained in connection with the attack – six in St Petersburg and two in Moscow – are also from Central Asia.