Russian President Vladimir Putin said on Thursday that a blast that ripped through a St Petersburg supermarket the previous day injuring shoppers was the result of an act of terrorism.

Putin was speaking at an awards ceremony in the Kremlin for Russian military servicemen and women who served in Syria.

"You know that yesterday in St Petersburg a terrorist act was carried out," Putin told the audience.

"And that recently the Federal Security Service prevented another attempted terrorist act."

Putin said the security situation in Russia would be much worse however if thousands of Russian citizens who had fought with Islamic State in Syria had been allowed to return home.