"Regarding the link with Islamic radicalism, we have to wait to know more until the investigation yields its full results", Abyldaev said at a press conference with Russian Foreign Minister Sergey Lavrov. A bomb blast tore through a subway train deep under Russia's second-largest city St. Peter.
The Federal Security Service, the main KGB successor agency, said in a statement that its experts defused a self-made explosive device at the apartment.
The people targeted in the search are "several citizens of Central Asian republics, who had been in contact" with suspected bomber, 22-year-old Akbarjon Djalilov, the committee said. A bomb also was found and disarmed in the apartment shared by the three suspects on the outskirts of St. Petersburg.
Veronika Skvortsova said in a televised briefing on Tuesday that 11 people died at the scene, one in an ambulance and two in hospital.
Jalilov's parents, who live in the southern Kyrgyz city of Osh, were questioned there by Kyrgyz authorities on April 4 and were then flown to St. Petersburg.
One victim of Monday's attack, 50-year-old Irina Medyantseva, an artist well-known for the dolls she made, was buried Thursday in a funeral attended by a few dozen relatives and friends. The Interfax news agency said authorities believe the suspect was linked to radical Islamic groups and carried the explosive device onto the train in a backpack.
Six people arrested after deadly St. Petersburg subway bombing
Investigators are apparently examining links between the arrested men and Monday's alleged bomber, 22-year-old Akbarzhon Jalilov. In the past two decades, Russian trains and planes have been frequent targets of attack, usually blamed on Islamic militants.
The six detained were accused of recruiting "mostly immigrants from the republics of Central Asia to commit crimes of a terrorist nature and involvement in the activities of terrorist organizations banned in Russian Federation", including the so-called Islamic State, the statement said.
Commuters on the busy Saint Petersburg metro remained on edge after the system temporarily shut down Monday in the wake of the attack. "The recent tragic events in St. Petersburg are the best confirmation of this", Putin said at the meeting in Moscow. Any terror attack that happens in the country is an attack on every single Russian citizen.
Authorities have not specified whether the attack was a suicide bombing or whether the bomber got away.
"I had no time to think about fear at that moment", he said.
That station is a major transfer point for passengers on two lines and serves the railway station to Moscow. Alexander Zhilkin, governor of the region, said the attackers are on the run.