MOSCOW: Russian investigators said Thursday they had searched a flat of acquaintances of the suspected Saint Petersburg metro bomber, as they probe the attack that left 13 people dead.
"Objects relevant to the investigation were found during the search of the apartment where these people lived," the Investigative Committee said. "They were all confiscated and sent for analysis."
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.
It did not disclose the nature of the objects confiscated.
Authorities said Wednesday they had searched Djalilov's residence and said CCTV footage showed him leaving his home ahead of the attack "with a bag and rucksack."
Investigators said Djalilov -- believed to be a Russian citizen born in the Central Asian nation of Kyrgyzstan -- had set off a bomb in a train carriage travelling between two busy Saint Petersburg metro stations on Monday afternoon.
His remains were found at the site of the blast and traces of his DNA were also discovered on a bag containing a bomb at another metro station that was successfully defused, investigators said.
No one has so far claimed responsibility for the attack.
The head of Russia's Investigative Committee Alexander Bastrykin has ordered officials to look into any potential "links" between the alleged attacker and the Islamic State group.
Jihadists from IS -- which includes foreign fighters from ex-Soviet Central Asia and the Caucasus region -- have repeatedly threatened an attack on Russian soil in revenge for Moscow's military backing of Syrian leader Bashar al-Assad.