ISIS-K, a branch of the Islamic State group, claimed responsibility for the attack. The US also said that the group was behind the attack, citing intelligence.
Russian state media said four suspects were identified as citizens of Tajikistan.
The suggestion that the attackers were from Tajikistan could create new tensions between the country and Russia.
Tajikistan has already tried to distance itself from the attack.
Its foreign ministry said Saturday reports that its citizens were involved were "fake," The Moscow Times reported .
The country's interior ministry also said that two of the suspects initially named by Russian media were in Tajikistan at the time of the attack, per The Moscow Times.
Meanwhile, Tajik President Emomali Rahmon told Putin on Sunday that "terrorists have no nationality, no homeland and no religion," his office said.
According to Mail Online , Rahmon said Tajikistan had to "beg" Russia to attend a forum in Tajikistan. "We are never being treated like strategic partners! No offense, but we want to be respected!" he said.
Some of these experts said CSTO members looked at the invasion of Ukraine and believed that Russia was now unlikely to be able to protect them, and may even decide to attack them.
The suspects in the attack being citizens of Tajikistan would not disprove ISIS involvement. Neither ISIS nor the US has commented on the nationality of the attackers, and ISIS has been recruiting in the country , The Guardian reported.
Russia is also going out of its way to point the finger at Ukrainian involvement. Putin said over the weekend that the assailants were fleeing to Ukraine after the attack and that Kyiv was helping them escape.
Russia watchers predicted when the attack started that Putin would try to blame Ukraine so he could avoid responsibility and use it to galvanize support for his war.
Experts also said that ISIS likely took advantage of Russia's distraction with the conflict in Ukraine. Vera Mironova, an associate fellow at the Davis Center at Harvard University, told the Financial Times that ISIS saw it as relatively easy to hit Moscow as a result.
Meanwhile, Ukrainian President Volodymyr Zelenskyy suggested that Russia could have stopped the attack if it weren't attacking Ukraine.
"Those hundreds of thousands of Russians who are now killing on Ukrainian land would surely be enough to stop any terrorists," he said.
just think what a great country we would have if ALL this fighting would stop. think of ALL the babies being killed they be great Leaders for your country some day. USE your head if you have one and think hard about it. PEACE is the answer. God is with us all.
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