A Kyrgyz-born Russian is suspected of being behind a suicide blast that killed 14 people and injured dozens of others on board a metro train in Saint Petersburg, Russia on Monday.
A spokesman for Kyrgyzstan's security service on Tuesday identified 22-year-old Akbarzhon Jalilov as the man suspected of being behind the attack.
"It is probable that he acquired Russian nationality," he said without divulging further details.
Kyrgyzstan is a Central Asian nation of 6 million. It is a close political ally of Russia and hosts a Russian military air base.
Russia has formed a special committee of investigators who will probe the assault as an "act of terror." It said it will be looking into all other possible causes as well.
Russia has announced three days of mourning for victims of the attack.
Russian President Vladimir Putin, who was in St Petersburg on Monday, visited the attack site.
International condemnation of the assault was swift.
US President Donald Trump spoke with the Russian president on Monday. He offered condolences and pledged Washington's "full support" for Moscow's response to the attack.
UN Secretary-General António Guterres condemned the explosion and called for those responsible to be held accountable.
British Foreign Secretary Boris Johnson said, "My sympathies are with the victims and their families."
TRT World's Sofia Baiburina has more from St Petersburg.