Russia's FSB state security service said on Wednesday it had detained the brother of the man suspected of orchestrating a terror attack which killed 14 people on the St. Petersburg metro this month, TASS news agency reported.

The FSB said Akram Azimov had helped transfer money, prepare for the attack and organize communication with "international terrorists", TASS reported.

Akram's brother, Abror, told a Russian court on Tuesday he was an unwitting accomplice in the April 3 attack.

Investigators said he had spoken with the suspected suicide bomber, Akbarzhon Jalilov, by telephone before the attack and helped mastermind the operation from a Moscow suburb.