Russian investigators have searched a St. Petersburg apartment where a number of citizens of unspecified Central Asian countries who reportedly had been in contact with subway bombing suspect Akbarjon Jalilov lived.
Federal Investigative Committee spokeswoman Svetlana Petrenko on April 6 said six people were detained in St. Petersburg and two were being held in Moscow in connection with the April 3 bombing that killed 14 people, including the suspected suicide bomber.
The names and nationalities of the detainees were not made public.
A committee statement said security forces had searched a St. Petersburg apartment where the men were living and seized a bomb, firearms, and ammunition. The bomb, it said, was "identical" to one that was found at the Ploshchad Vosstania metro station on the day of the deadly attack.
The investigation into the blast, which also injured 50 people, continued as thousands gathered in officially sanctioned events in St. Petersburg, Moscow, and other cities to remember the victims.
WATCH: Muscovites Show Solidarity With St. Petersburg After Attack
There has been no claim of responsibility for the blast.
However, the Investigative Committee on April 4 said it had determined that Jalilov, 22, set off a bomb that exploded on a subway train between two stations in central St. Petersburg and that his remains were found at the scene.
Traces of his DNA were also found on a bag containing the bomb that was successfully defused at the Ploshchad Vosstania station, investigators said.
Jalilov was an ethnic Uzbek who was born in Kyrgyzstan and held Russian citizenship.
Authorities are also investigating any links between the bombing and the Islamic State (IS) extremist group, which has claimed responsibility for several deadly attacks in the Middle East and Europe.
IS on April 6 claimed responsibility for a separate attack this week that killed two Russian traffic-police officers in the southern city of Astrakhan.
Meanwhile, people clutching flowers and white balloons gathered outside St. Petersburg's Tekhnologichesky Institut subway station, near where the train was traveling when the bomb exploded.
"I came to show that we will not be frightened," Valentina Zlobina, 48, told the AFP news agency. "We will become even more united in this tragedy."
The first funeral for a victim of the blast was held outside of St. Petersburg on April 6.
About 50 people gathered to mourn the death of 50-year-old puppet maker Irina Medyantseva. She was on the subway train with her daughter, Yelena, who is recovering in a hospital.
"We had just bought a flat near here in a beautiful building. Our daughters were doing well, and then this happened," her husband, Aleksandr Kaminsky, told AFP.