A loud explosion has been heard in a residential building in St Petersburg close to a site where explosives were found earlier in the day.
No one was hurt in the blast, which caused masonry to fall from the building onto a vehicle, damaging it, state news agency RIA Novosti reported, citing an unnamed official in the country's emergencies ministries.
In the early hours of the morning (6 April) investigators raided a flat in the city's Tovarichesky Prospekt district, as part of a probe launched following Monday's explosion on the city's metro, that killed 14 people.
Residents of the block were evacuated when police found an unexploded bomb similar to that used in Monday's attack.
Russia's domestic security service, the FSB, said in a statement to Russian media agencies that its experts had defused a home-made explosives device in the flat.
The person who carried out the attack has been named as Kyrgyzstan-born Akbarzhon Jalilov, 22, who died in the explosion. Jalilov worked in St Petersburg and had Russian citizenship.
Three people have been arrested in the former Soviet central Asian country in connection with the investigation, said Russia's Investigative Committee.
On Wednesday, security services arrested six people in St Petersburg accused of recruting for jihadist groups Isis and Jabhat al-Nusra, a former affiliate of al-Qaeda in Syria.