A suicide bomber from Kyrgyzstan was behind the explosion that killed 11 people and injured dozens more in the Saint Petersburg metro, security services in the Central Asian country said Tuesday.

“The suicide bomber in the Saint Petersburg metro was a Kyrgyz national Akbarjon Djalilov… born in 1995,” a spokesman for the country’s security services told AFP. “It is probable that he acquired Russian nationality.”

According to Russia’s state-funded RT news service, a Russian citizen of Kyrgyz origin was “possibly” the bomber, though there has been no official confirmation.

Russia’s Investigative Committee said it was probing an “act of terror” over the blast that rocked the metro in the country’s second-largest city on Monday afternoon, but added it would look into all other possible causes of the blast.

There was no immediate claim of responsibility for the explosion, which came after the Islamic State group called for attacks on Russia in retribution for its military intervention in Syria against the jihadists.

The predominantly Muslim country of Kyrgyzstan is a close ally of Russia, and depends on its neighbor for financial support. The Russian air force has a base in the country and there is a joint military base for the two militaries in the country’s largest city of Bishkek.

Saint Petersburg’s metro reopened on Tuesday following its closure after Monday’s blast.

The blast occurred in a train carriage as it was traveling between the Technological Institute and Vosstaniya Square stations at 2:40 p.m., said antiterrorist committee (NAK) spokesman Andrei Przhezdomsky.

The NAK committee later confirmed security services had found another explosive device at the Vosstaniya Square metro station. This device did not explode and was immediately “neutralized.”

Russian President Vladimir Putin, who had been in Saint Petersburg holding a meeting at his Strelna presidential palace, offered condolences to the wounded and to the loved ones of those killed.

At least 7,000 nationals from former Soviet countries, including 2,900 Russians, have joined jihadist groups in Iraq and Syria, mostly IS, according to Russia’s FSB intelligence service.

Russia has not been hit by an apparent attack this deadly since the bombing of a plane carrying vacationers back to Saint Petersburg from the Egyptian resort of Sharm el-Sheikh in October 2015, which was claimed by Islamic State. All 224 people on board were killed.

Russian ground transport has also been hit by extremists before.

In 2013, twin suicide strikes within two days at the main railway station and a trolleybus in the southern city of Volgograd — formerly known as Stalingrad — claimed 34 lives and raised alarm over security at the Sochi Winter Olympic Games.

A suicide raid on Moscow’s Domodedovo airport claimed by Islamic insurgents from the North Caucasus killed 37 people in January 2011.