The suspect in Monday's train explosion in St. Petersburg, Russia, which killed 11 people and injured dozens, has been identified by Kyrgyz security services, according to several news agencies.
The suspect, named as Akbarjon Djalilov, is a Kyrgyzstan national.
A three-day mourning period for the victims has begun. Four people remain in critical condition, the Health Minister said. Russian President Vladimir Putin held a meeting with security and law-enforcement services. US President Donald Trump spoke briefly with Putin, expressing his condolences. Putin laid roses at one of the memorials Tuesday. The President had been in St. Petersburg on Monday before the attack. Some metro stations are reopening after a complete network shutdown.
The explosion took place between the Sennaya Ploshchad and Tekhnologichesky Institut stations at about 2.40 p.m. on Monday. Photographs from the scene showed bandaged and bloodied bodies being carried from the station where the train came to a stop.
Others showed bodies lying by the train itself at Tekhnologichesky Institut as the station filled with smoke.
Four of the injured are in critical condition, Health Minister Veronika Skvortsova said, according to TASS.
Russians laid flowers and tributes at memorials as a three-day mourning period has begun.
No group has claimed responsibility for the attack, which led to the shutdown of the city's metro system.
Russian Prime Minister Dmitry Medvedev described the attack as a "terrorist act," but authorities have released no specifics on who they believe is responsible.
A second, larger device was found and defused at another station, Russia's Anti-Terrorism Committee said.
That device, hidden in a fire extinguisher, was larger than the one that went off, according to state media reports quoting law enforcement. It carried about a kilogram of TNT, the reports said.
No claim of responsibility
Analysts have speculated that the bomber could be affiliated with either a Chechen separatist group or ISIS. ISIS claimed the bombing of a Russian MetroJet flight over the Sinai desert in Egypt, which killed all 224 people aboard.
Another possibility, says former CNN Moscow Bureau Chief and Woodrow Wilson Center Global Fellow Jill Dougherty, is a hybrid Chechen rebel-ISIS attack.
Many Chechen fighters have gone to fight in Syria, she said, and it has long been feared that they could bring their battlefield expertise back home.
"The fear was that after (Chechens) had been radicalized and almost professionalized, by that time in Syria would then come home and carry out attacks in Russia ... (which) would fit the kind of ISIS international terrorism theory that Putin has been talking about," she said.
"It makes it easier for him to make that proposal... to President Trump and the West -- 'let's get on board, lets fight terrorism together.'"
However, former FBI special agent Bobby Chacon says that to stay silent after an attack goes against the ISIS modus operandi.
"The first thing that's missing from an investigator's perspective is the claim of responsibility," he told CNN.
"Last year when two ISIS operatives attacked police officers on the outskirts of Moscow... one of the first things that was released was the video where they claimed allegiance to al Baghdadi, the ISIS leader and ISIS itself and that's a hallmark, as we've seen in San Bernardino, of an ISIS attack."
Russia was once a hotspot for terror attacks, but the country has experienced relatively few in recent years.
In December 2013, a suicide bombing at a train station in Volgograd killed at least 16 people. The following day, in the same city, a suicide bombing on a trolley bus killed 14 people.
In 2010, two female suicide bombers linked to the Chechen insurgency blew themselves up at two Moscow metro stations, killing 40. In 2002, Chechen rebels killed 170 hostages in a theater in the capital, Moscow.