ST. PETERSBURG, Russia — A likely suspect in the blast that ripped through a subway car in St. Petersburg Monday, killing 14 people, is a Russian citizen born in a restive region of Kyrgyzstan, the Central Asian country’s security service said Tuesday.

The state security service of Kyrgyzstan identified the suspect as Akbarzhon Dzhalilov, who was born in the city of Osh in 1995, the Interfax news agency reported. The service said it was working with Russian law enforcement, who are investigating the incident as an act of terrorism.

Osh was the site of bloody fighting between ethnic Kyrgyz and Uzbeks in 2010. The city is located in the Ferghana Valley, an area shared by three former Soviet republics that is known as a breeding ground for extremism in Central Asia.

The security agency said it was checking when Dzhalilov left Kyrgyzstan.

An updated toll from Russian authorities said that 51 people were injured when an improvised bomb went off in the train as it traveled between two central St. Petersburg stations. In the subway station located at St. Petersburg’s main railway station, authorities later found another explosive device that had not detonated and disarmed it.

The blast in Russia’s second-largest city cut across the fault lines of a country grappling with its first signs of political upheaval in years.

Some government opponents expressed concern Monday that the Kremlin might use the attack as an excuse to curtail a nascent movement that brought tens of thousands of people into the streets eight days earlier to protest official corruption.

In fact, President Vladimir Putin reminded Russians last week that what started as street protests calling for reforms in Ukraine and the Arab Spring countries, degenerated into violence and bloodshed.

Later on Monday, Putin placed a bouquet of roses at the subway station where the train came to a halt after the blast. Russian authorities credit the driver, who kept the train moving until it reached the Tekhnologichesky Institute station, with saving the lives of passengers who otherwise might have been trapped. Earlier, Putin expressed condolences to the victims’ families in televised remarks.

Above ground, people had made a makeshift memorial outside Sennaya Ploshchad station, the busy central interchange from which the train departed before the bomb went off.

The blast in one of the St. Petersbrug’s most celebrated, and tourist-visited, neighborhoods, shook the city and ignited anger among ordinary residents. The area around the Sennaya Ploshchad station is near some of the most famous sights and was the setting of Fyodor Dostoevsky’s novel “Crime and Punishment.”

“Shock, I felt shock. It’s disgusting,” said Andrei Gontarevsky, 51, who said he manages a small team of construction workers. “It’s unthinkable. This was always a quiet city, and I think it shows the times are turning bad now.”

Shortly after the blast, the entire St. Petersburg subway system was shut down for a time as a precaution, and security was heightened around the city, where Putin was holding talks with Belarusan leader Alexander Lukashenko.

Authorities said the blast was caused by an improvised explosive device that went off in one of the cars as the train traveled from Sennaya Ploshchad about 2:40 p.m.

Islamist militants from the North Caucasus have been blamed in more than a dozen major terrorist attacks in Russia since the country fought two civil wars in Chechnya. Russia still faces a simmering insurgency in the neighboring Dagestan province, and in March, six Russian soldiers and six militants were killed in a shootout in Chechnya.

But the post-Soviet republics of Central Asia have also been a source of Islamist fighters.

And Moscow’s military involvement in Syria, which included heavy aerial bombardments of areas controlled by forces rebelling against that country’s president, Bashar Assad, has also made Russia a target of the Islamic State. Russian officials have concluded the October 2015 midair explosion of a Russian jetliner over Egypt’s Sinai desert that killed all 224 people aboard was the result of a terrorist attack.

The city of St. Petersburg announced three days of mourning beginning Tuesday. The U.S. Embassy in Moscow joined other countries in expressing condolences.

In Washington, President Donald Trump called the incident a “terrible thing.” He called Putin to express his condolences, according to Putin’s spokesman.

In Moscow on Tuesday, riot police with bomb-sniffing dogs were patrolling outside Kievskaya Metro station, the interchange for three subway lines. Police and security guards had stepped up their vigilance at the metal detectors at the entrances to the subway, hotels, and shopping malls.