The prime suspect in Monday's bomb attack on the St Petersburg metro is a Russian citizen born in the former Soviet republic of Kyrgyzstan, according to Kyrgyz intelligence.
Russia's health minister raised the death toll from 11 to 14 on Tuesday and said 49 people were still in hospital. She said 11 people had died at the scene, one died while being transported by ambulance and a further two died in hospital.
Kyrgyzstan's state committee for national security said 22-year-old Akbarzhon Jalilov could be behind the attack, and that it was cooperating with Russian agencies to help investigate.
Russian investigators said they believed the attack was carried out by a suicide bomber, based on some of the body fragments they found at the scene. Investigators said they had identified the bomber but would not release details at this stage.
A Kazakh man named by some media outlets as a potential suspect overnight appears to have been one of the victims, while a man whose photograph was widely circulated by Russian media on Monday went to police to state his innocence.
A second bomb left at a different station did not detonate and was defused. It was unclear if both bombs were left by the same person or if others were involved.
News agencies reported that the suspect, Jalilov, had lived in Russia for six years and was from the city of Osh in southern Kyrgyzstan. There are hundreds of thousands of Central Asians living in Russia, who often work on construction sites in poor conditions, sending the money they earn to their families back home.
Late on Monday night, president Vladimir Putin held a meeting with security chiefs. He took a phone call from Donald Trump in the early hours of Tuesday.
"President Trump offered the full support of the United States government in responding to the attack and bringing those responsible to justice," a White House statement said. "Trump and President Putin agreed that terrorism must be decisively and quickly defeated."
For many years, Russia suffered frequent terror attacks from Islamist groups based in the North Caucasus, including blasts on the Moscow metro in 2010. However, since a suicide bomber struck at Domodedovo airport in January 2011, attacks have largely been confined to the North Caucasus itself.
Since Russia entered the war in Syria in September 2015, a number of Islamic State propaganda outlets have said the country would be a target. In October 2015, a plane travelling from Sharm el-Sheikh in Egypt to St Petersburg crashed, apparently after an explosive device was detonated on board. Isis claimed responsibility.
Monday's explosion occurred at about 2.30pm local time, after the metro train had left Sennaya Ploshchad station in the centre of St Petersburg. The driver decided to continue to the next station, Tekhnologicheskii Institut, in order to make evacuation easier.
On Tuesday, the train's driver, Alexander Kaverin, told Russian media how he had made the decision: "There was a bang, and dust. I made contact with the controller and explained the situation. Then I started getting incomprehensible messages on the intercom system, from all the carriages at once. I made the decision according to the rules for such emergencies, to continue on to the next station."
In the hours after the blast, Russia's anti-terror agency said a second bomb had been found and defused at Ploshchad Vosstaniya, another metro station in the centre of the city. Interfax said the second bomb would have been several times more powerful than the first, and was reportedly a device disguised as a fire extinguisher that had been rigged with shrapnel.