"The subject is active on the agenda and, of course, it requires an increased level and scope of work from special services," Dmitry Peskov told reporters.
On Monday, an explosion occurred in St. Petersburg in a subway train car on the stretch between the Sennaya Ploshchad and Tekhnologichesky Institut metro stations. Another blast that was supposed to take place on the Ploshchad Vosstaniya station was prevented by bomb technicians.
The explosion claimed the lives of at least 14 people, 55 others remain in hospitals, some are in critical condition.
The Russian Investigative Committee has opened a criminal investigation into the suspected terrorist attack in the St. Petersburg metro but it is also following other leads.