Russian authorities say that six citizens of Central Asian states have been detained in St. Petersburg on suspicion of recruiting for Islamic militant groups.
The federal Investigative Committee said that there was no evidence "at this time" of any connection between the people detained on April 5 and the Kyrgyz-born suspect in the April 3 subway bombing that killed 14 people in St. Petersburg.
In a statement, the investigators said the detainees had come to Russia to work.
It said they were suspected of recruiting other migrants from Central Asia "to carry out terror-related crimes" and join extremist groups that are banned in Russia, including Islamic State (IS) and the Al-Nusra Front.
WATCH: Russian authorities have named Akbarjon Jalilov as the main suspect in the deadly bombing in the St. Petersburg metro on April 3. Some of Jalilov's former schoolteachers in Osh, Kyrgyzstan, spoke to RFE/RL and described what he was like. (Current Time TV/RFE/RL's Kyrgyz Service)
The statement said the authorities had not yet decided whether to press charges against the detainees.
The identification of Kyrgyz-born ethnic Uzbek Akbarjon Jalilov as the bombing suspect stoked fears of police action targeting migrants from Central Asia and the Caucasus.
The Investigative Committee said the six Central Asian citizens were detained as part of a joint operation by investigators, the Federal Security Service (FSB), the Interior Ministry, and the National Guard.
Bombing Suspect's Home Searched
In a separate statement released earlier on April 5, the committee said investigators had searched the home where Jalilov lived and had questioned about 40 witnesses.
It said surveillance cameras had captured the moment when he left his building carrying a bag and a knapsack.
The committee said on April 4 that it had determined that Jalilov, 22, set off a bomb that exploded on a subway train between two stations in central St. Petersburg the previous day, and that his remains were found at the scene.
Russia's top investigative body said DNA evidence indicated that Jalilov also placed a bag containing a bomb at another subway station on April 3. That device was defused.
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.
The suspect's mother, Odinakhon Jalilova, told journalists at the St. Petersburg airport, "I do not believe he did it."
WATCH: Residents of St. Petersburg pulled together following the deadly bombing on the Russian city's subway system on April 3. Dozens of people showed up at a hospital to donate blood for the survivors of the blast. (RFE/RL's Russian Service, Current Time TV, Reuters)
Later on April 5, Russian President Vladimir Putin told senior security officials from countries in the Commonwealth of Independent States (CIS) that the subway bombing showed that former Soviet republics continue to face a threat from terrorism.
"We see that, unfortunately, the situation is not improving. The recent tragic events in St. Petersburg are the best confirmation of this," Putin said at the meeting in Moscow.
"We know that each of our countries, practically every one, is a possible and potential target of terrorist attacks," he said.
Uzbek President Shavkat Mirziyaev, meeting separately with Putin, said that the bombing "once again signals that we should take very tough measures together" to combat terrorism.
Mirziyaev, who became president after the death of longtime autocrat Islam Karimov was announced in September, said Uzbekistan was prepared to cooperate closely with Russia on security issues.
With reporting by RFE/RL's Kyrgyz and Uzbek services, AP, Reuters, TASS, Interfax, and RIA Novosti