MOSCOW - Russia has opened a terror attack investigation into an explosion that resulted in two deaths, including a senior military official, the Russian Investigative Committee said Tuesday.

Investigators are conducting a criminal investigation into murder, terrorist acts, and the illegal circulation of weapons and ammunition "in connection with the death of two servicemen in the capital", the committee said in a statement.

Earlier in the day, Lieutenant General Igor Kirillov, head of the Russian Armed Forces' radiological, chemical and biological defense troops, and his assistant were killed by an explosion in a residential building in Moscow.

The committee had previously said it opened a criminal case, adding the blast occurred after the detonation of an explosive device planted in a scooter parked next to the entrance of the residential building.