Russian President Vladimir Putin on Thursday said a bomb that went off in a St. Petersburg supermarket on Wednesday was an act of terrorism.

"You know that yesterday in St. Petersburg a terrorist act was carried out," Putin said, referring to the explosion that injured at least 13 shoppers in a branch of the Perekrestok supermarket chain.

Read more: 'Homemade' bomb injures several people at St. Petersburg supermarket

Putin made the comments at an awards ceremony in the Kremlin for Russian personnel who had served in Syria. He told the audience security forces should take no chances with their own lives if confronted by terrorist suspects.

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

Read more: Syria conflict: What do the US, Russia, Turkey and Iran want?

Russian intelligence, the Federal Security Service, had "recently thwarted another attempted terror attack," Putin added. He did not provide further details but the Kremlin said earlier this month that a US tip-off had helped thwart a planned attack on St. Petersburg's Kazansky Cathedral.

Read more: Group with alleged al-Qaeda ties claims St. Petersburg metro bombing

The Federal Security Service said seven suspects linked to IS were arrested in connection to that alleged plot.

In April, a suicide bombing in St. Petersburg's subway left 14 people dead and dozens wounded. Russian authorities identified the bomber as a 22-year old Kyrgyz-born Russian national.

law/rt (AFP, AP, dpa, Reuters)