St Petersburg residents laid flowers at a makeshift memorial outside the entrance to the Sennaya Ploshchad metro station on Tuesday (April 4) to pay tribute to the victims of a blast in a St Petersburg train carriage on Monday (April 3) that kill 11 people and wounded 45.

Russia’s Interfax news agency, quoting an unidentified law enforcement source, said that human remains examined at the scene suggested that the blast had been carried out by a suicide bomber.

It said the police had identified a suspect with links to radical Islamist groups banned in Russia.

There was no immediate claim of responsibility. Officials said they were treating the blast as an act of terrorism, but there was no official confirmation of any link to Islamist radicals.

The National Anti-Terrorist Committee said an explosive device had been found at another station, hidden in a fire extinguisher, but had been defused.