St Petersburg metro blast in Russian Federation on April 3, suspected to be carried out by suicide bomber identified as Akbarjon Djalilov from Kyrgyzstan, has left 14 people dead and about four dozen injured, as per media reports.
Three people have been arrested over suspected links to the suicide bomber who attacked St Petersburg's subway.
The Investigative Committee said the seven suspects had tried since November 2015 to recruit others from central Asia to carry out "crimes of a terrorist nature", and to join the jihadist groups Fateh al-Sham Front and Isis.
President Vladimir Putin, who was visiting the city on an unrelated trip Monday, said investigators were looking into whether the explosion was a terror attack or if there might have been some other cause.
Kyrgyz authorities have so far failed to turn up evidence of links between Jalilov and Islamist radicals, sources in the capital, Bishkek, and in Osh told Reuters.
Authorities said they had definitively identified all 13 victims of the attack, and had also confirmed Djalilov's fragmented remains using DNA tests.
"First, I was really scared", said Viktoria Prishchepova, one who did take the subway.
US President Donald Trump called Mr Putin to offer condolences over the attack.
Investigators said that extremist literature had been discovered in a search of the living quarters of the men.
The 22-year-old Jalilov, who worked at a garage in St. Petersburg, was born in the Central American country of Kyrgyzstan, but obtained Russian nationality in 2011.
A man lays flowers in memory of victims of the blast in the Saint Petersburg metro at a memorial stone reading Leningrad by the Kremlin wall in central Moscow on April 3, 2017.
There has been no claim of responsibility.
The killer's parents flew overnight to Russian Federation from their native Kyrgyzstan to help a probe that needs to clarify if he was working alone or is part of a terror group plotting other explosions.
The foreign ministry of the former Soviet republic of Kazakhstan says a Kazakh citizen was among the 14 killed in Monday's blast on the St. Petersburg subway. Tass said he reportedly flew to Turkey in November 2015 and spent a long time overseas.
Russia's state investigative committee said the detainees had been charged with aiding terrorist activity.
Monday's explosion occurred as the train travelled between stations on one of the city's north-south lines.
Separately, a homeless Russian man was injured on Thursday when a homemade device placed in a bag near a school exploded in the southern city of Rostov-on-Don, according to local media.
Isachenkov reported from Moscow.