MOSCOW - A Russian lieutenant general and his assistant were killed by an explosion in a Moscow residential building on Tuesday morning.

Lieutenant General Igor Kirillov, head of the Russian Armed Forces' radiological, chemical and biological defense troops, was killed in the explosion, said the Russian Investigative Committee.

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Preliminary information showed the explosion occurred after the detonation of an explosive device, which had a power of about 200 grams of TNT.

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The explosive device was planted in a scooter, said the committee, adding that a criminal case has been opened in connection with the killing.

Terror attack probe

The committee later said it has opened a terror attack investigation into the explosion.

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.