ST. PETERSBURG, Russia -- Russian President Vladimir Putin has told security officials from a regional alliance that this week's subway bombing in St. Petersburg underlines that terrorism's threat is not subsiding.
Putin met Wednesday with heads of the security services from the Commonwealth of Independent States, a grouping of most former Soviet republics. The meeting came two days after a bomb blast on a subway in Russia's second-largest city killed 14 people. The bomb went off Monday afternoon as the train was moving between two stations.
"We see that, unfortunately, the situation is not improving. The recent tragic events in St. Petersburg are the best confirmation of this," Putin said. "We know that each of our countries, practically every one, is a possible and potential target of terrorist attacks."
Russia's top investigative body said six people have been arrested in St. Petersburg on suspicion of "aiding terrorist activities."
The Investigative Committee said in a statement on Wednesday that the men arrested come from former Soviet Central Asian republics. The investigators suspect that they have been recruiting Central Asian men to join the ranks of the Islamic State group and other extremist organizations in St. Petersburg since November 2015.
The statement Wednesday stated: "At this moment the investigators have no evidence of connection or acquaintance of the detained with executor of the terrorist action in the St. Petersburg metro."
The parents of the suspected suicide bomber in Monday's deadly explosion have arrived in St. Petersburg for questioning.
State-owned Rossiya 24 television on Wednesday showed footage of a middle-aged woman in a red coat and a white headscarf and a man in a black jacket, chased by journalists.
Akbardzhon Dhzalilov, 22, is believed to have moved to St. Petersburg from the Central Asian nation of Kyrgyzstan when he was a teenager.
One of those stations was closed by a bomb threat Tuesday and again on Wednesday as officials checked for anything suspicious.
Investigators say they have searched the home of the suspected suicide bomber.
The Investigative Committee said in a statement in the early hours on Wednesday that the investigators searched the man's home in St. Petersburg. They also examined CCTV footage from outside Dzhalilov's home which shows him leave home with a bag and a backpack.
Another bomb, hidden in a bag, was found and de-activated at another St. Petersburg station just half an hour before the blast. Dzhalilov's DNA was found on the bag.