Updated: 8:00 p.m. ET

(Bloomberg) – A subway bombing in St. Petersburg killed 11people and injured dozens more during a hometown visit by PresidentVladimir Putin, officials said, renewing fears of terrorism in Russia's biggestcities less than a year before presidential elections.

A homemade device filled with shrapnel detonated inside a trainbetween two central hubs at about 2:40 p.m., the NationalAnti-Terror Committee said. Footage from the Sennaya Ploshchadstation about a mile from the Hermitage Museum showed carriagedoors blown open, with bloodied and dazed passengers lying on theunderground platform amid billowing smoke.

Officials called the blast, and the planting of a more powerfulbomb that was later defused at a nearby station, an act of terrorism, though investigatorscautioned that other possible causes can't be ruled out. Police arehunting for two suspects they believe planted the two devices, theInterfax news service reported, citing an unidentified lawenforcement official.

“All the signs of a terrorist attack are there,” Viktor Ozerov,head of the security committee in the upper house of parliament,said by phone from Moscow. “The complex of measures againstterrorism in the country failed.”

U.S. President Donald Trump, asked about the blast by reportersat the White House, called it a “terrible, terrible thing— happening all over the world.” Kremlin spokesman DmitryPeskov said later that the bombing was being discussed with theWhite House through diplomatic channels.

High alert

Officials in St. Petersburg, a city of 5 million people, shutdown the entire subway system, forcing thousands of commuters ontothe streets and snarling traffic as emergency vehicles struggled toreach the scene. They also ordered security to be enhanced atairports and other major transport nodes, measures that wererepeated in the capital Moscow.

In addition to the 11 who died, 45 injured people were beingtreated in hospitals, a spokesman for Russia's NationalAntiterrorism Committee said on Rossiya 24 state television.

Putin visited the Federal Security Service's St. Petersburgbranch to be briefed on the subway attack by security agencies,Interfax reported, citing Peskov.

Russia's two biggest cities haven't suffered a major attack inmore than five years. The Kremlin tightened security after hundredswere killed by terrorist strikes in the early 2000s that were laterclaimed mostly by Chechen separatists. Since Putin sent forces intoSyria in 2015, Islamic State has threatened to strike at Russia,taking responsibility for the downing of a plane carrying Russiantourists from Egypt to St. Petersburg, which left 224 dead.

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Suicide bombers attacked the capital's subway system incoordinated attacks in 2010 that claimed 40 lives. The last majorattacks took place in December 2013, just weeks before the SochiWinter Olympics, when 30 people died in strikes on a train stationand a bus in Volgograd.

Islamic State has vowed to take revenge for Putin's bombing inSyria and has claimed responsibility for some attacks in Russia'smainly Muslim North Caucasus region. Russian-speaking jihadistsmake up the largest foreign contingent of Islamic State fighters inSyria and Iraq, according to the Institute for InternationalStudies in Moscow.

'Barbaric acts'

“These barbaric acts once again show that the terrorists' maingoal is to sow fear and uncertainty and cause instability insociety,” Boris Gryzlov, a top official in the ruling United Russiaparty and a former interior minister, said after Monday's attack,according to Tass.

The bomb used in the subway attack appeared to have had a timer,not detonated by a suicide bomber, Interfax reported, citinginvestigators. It exploded with a force equal to about 300 grams ofTNT, just one-fourth of what was used in the device that wasdisarmed, the news service said.

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Some political analysts said the Kremlin may seek to capitalizeon the bombing like it has with previous terrorist attacks,particularly after the biggest anti-Kremlin protests in severalyears swept major cities on March 26.

“Experience in Russia shows that the terrorist threat can serveas a justification for political tightening, such as banning massdemonstrations,” said Valery Solovei, who teaches at Moscow's mainuniversity for diplomats. “But I don't think the security issuewill get the authorities very far this time. People are used toliving under the risk of terror.”

Russia is due to hold presidential elections in less than ayear. Putin, in power since 2000, is widely expected to seek afinal, six-year term.

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