The Kremlin said on Monday that the assassination of prominent war blogger Vladlen Tatarsky in St. Petersburg was a "terrorist act" and cited Russia's Anti-Terrorism Committee in saying that there was evidence linking Ukraine to the bombing.

In a call with reporters, Kremlin spokesman Dmitry Peskov referred to a statement by the Committee, adding, "This is a terrorist act."

"The active phase of the investigation is now under way," he said. "We see quite vigorous steps to detain suspects. Let's be patient and wait for the next announcements from our special services, which are working on this."

Separately on Monday, the Interior Ministry announced it had detained Darya Trepova, whom it had previously named as a suspect in the attack.