MOSCOW (AP) — The explosion at a supermarket in Russia's second-largest city was a terror attack, President Vladimir Putin said Thursday, adding that he has ordered security agencies to kill terror suspects on the spot if they resist arrest.

Officials said 13 people were injured Wednesday when an improvised explosive device went off at a storage area for customers' bags at the supermarket in St. Petersburg. Investigators said the device contained 200 grams (7 ounces) of explosives and was rigged with shrapnel to cause more damage.

While Russian law enforcement agencies stopped short of immediately describing the blast as a terror attack, Putin did not mince words Thursday at a Kremlin awards ceremony for Russian troops who fought in Syria.

"You know that yesterday a terror attack was conducted in St. Petersburg," Putin said. He went on to note that another attack was thwarted recently, a reference to an alleged series of bombings in St. Petersburg that a CIA tip helped prevent, according to the Kremlin.

Putin said he told the chief of Russia's main domestic security agency, the FSB, that agents who encounter resistance from terror suspects should "liquidate bandits on the spot."

No one has claimed responsibility for the supermarket bomb. Eight of the injured remained hospitalized.

Putin's spokesman, Dmitry Peskov, would not offer any specifics on what led Putin to declare the attack an act of terrorism. The shrapnel that was part of the explosive device proved the explosion "was a terror attack anyway."

Storage boxes at all Perekrestok supermarkets in St. Petersburg were removed following the attack. Other chains said they would tighten security measures.

Earlier this month, Putin telephoned President Donald Trump to thank him for what the Kremlin described as a CIA tip that prevented more bombings in St. Petersburg, Putin's hometown.

The Federal Security Service said seven suspects linked to the Islamic State group were arrested in connection to the alleged plot. The Kremlin said the suspects had planned to bomb Kazan Cathedral and other crowded sites.

In April, a suicide bombing in St. Petersburg's subway left 16 people dead and wounded more than 50. Russian authorities identified the bomber as a 22-year old Kyrgyz-born Russian national.

During his remarks at the Kremlin awards ceremony, Putin said Russia's 2-year military campaign in Syria helped eliminate militants who threatened Russia.

He has previously said that over 4,000 citizens from Russia and some 5,000 people from other ex-Soviet nations have joined the Islamic State group in Syria and Iraq.