Donald Trump sends condolences to Putin after St Petersburg train bomb
The blast ripped through subway killing 11 and wounding 45
US president Donald Trump has called Vladimir Putin to offer condolences over the St Petersburg tube bombing.
The Kremlin said Mr Trump offered sympathy to the families of the victims of Monday's blast and asked President Putin to convey his support for the Russian people.
Mr Putin thanked Mr Trump for the expression of solidarity, the Kremlin said, adding that the two leaders voiced a shared view that "terrorism is an evil that must be fought jointly".
The blast ripped through an underground train in St Petersburg, Russia's second-largest city, killing 11 and wounding 45.
Mr Putin was visiting the city, his home town, at the time.
The United Nations Security Council condemned "in the strongest terms the barbaric and cowardly terrorist attack".
Council members "expressed their deep sympathy and condolences to the victims of this heinous act of terrorism and to their families, and to the people and to the government of the Russian Federation", a statement said.
It added that the "perpetrators, organisers, financiers and sponsors of these reprehensible acts" should be brought to justice.
Mr Trump said it was "absolutely a terrible thing", White House press secretary Sean Spicer said. He said the US was prepared to offer assistance to Russia.
There was no immediate claim of responsibility for the attack. In the past two decades, Russian trains and planes have been frequent targets of terrorism, usually blamed on Islamic militants.
The chaotic scene left victims sprawled on a smoky platform and hours later, anguish and fear rose again when police found and defused a shrapnel-packed explosive device at another St Petersburg station.
News reports initially said police were searching for two suspects and state television showed a photo of one man wearing what appeared to be a skullcap characteristic of Russia's Muslim regions.
But Interfax news agency later cited unspecified sources as saying police now suspected the blast was the work of a suicide bomber linked to radical Islamists.
Until now, St Petersburg, a major tourist destination famed for its imperial palaces and lavish art museums, had been spared attacks.
"From now on, I will be scared to take the subway," said Marina Ilyina, 30, who brought flowers to the station where the train stopped after the bombing.
"We in St. Petersburg thought we wouldn't be touched by that."
The explosion occurred in the mid-afternoon as the train travelled between stations on one of the city's north-south lines.
The driver chose to continue on to the next stop, Technological Institute, a decision praised by the Investigative Committee as aiding evacuation efforts and reducing the danger to passengers who would have had to walk along electrified tracks.
The National Anti-Terrorism Committee said the death toll was 11, with another 45 people being treated for wounds in hospitals.
Amateur video broadcast by Russian TV showed people lying on the platform of the Technological Institute station, and others bleeding and weeping just after the damaged train pulled in.
Within two hours of the blast, authorities found and deactivated another bomb at another busy station, Vosstaniya Square, the anti-terror agency said.
That station is a major transfer point for passengers on two lines and serves the railway station to Moscow.
Interfax cited an unidentified law enforcement official saying that investigators think the suspected suicide bomber left the device at Vosstaniya Square station before blowing himself up on the train.
The agency said authorities believe the suspect, a 23-year old who came from ex-Soviet Central Asia and was linked to radical Islamist groups, carried the explosive device on to the train in a rucksack.
Security was immediately tightened at all of the country's key transportat sites, including the Moscow tube network.
Mr Putin later laid flowers outside the Technological Institute station.
St Petersburg residents responded with both dismay and determination.
"They won't succeed in breaking up our country. We are all citizens of one country despite various political views and religious beliefs," said Alexander Malikov, 24, who brought flowers and candles to an improvised memorial outside one of the stations.
Lebanon's militant Hezbollah group, which is backing Syrian president Bashar Assad's forces along with Russia, says the incident was the type of "terrorism" Russia was fighting in Syria.
Most of the terrorist attacks in Russia have been connected to the uprising in Chechnya and other Caucasus republics in the southern part of the country.
The last confirmed attack was in October 2015 when Islamic State militants downed a Russian airliner heading from an Egyptian resort to St Petersburg, killing all 224 people on board.