Russia's FSB security service said today it had detained a suspected organiser of last month's bombing of the Saint Petersburg metro that killed 14 people and injured dozens more.
He has been identified as Abror Azimov, who was born in 1990 and is from Central Asia.
It said the suspect is accused of being involved in the attack and training the suicide attacker.
Russian authorities said the man was detained in the town of Odintsovo and was being questioned.
During raids of the detainees' departments, police said they found guns, ammunition and an explosive device similar to that used on the metro. Security forces said they safely defused another device left on a platform.
Azimov was detained on Monday in the Moscow region, the agency reported. Azimov, 27 years old, who was interrogated by the Russian Investigations Committee, is a member of the group of people involved in an attack with dynamite that was carried out on April 3.
After the bombing, President Vladimir Putin held talks with world leaders including US President Donald Trump to push for greater cooperation in the fight against terrorism.
Earlier, Russian media reported that the bomber had made a telephone call to someone in Moscow before the attack.