Ukraine claims it's behind Moscow blast that killed head of Russia's nuclear defense forces

Moscow — The head of Russia's Nuclear, Biological, and Chemical Defense Forces, Lt. General Igor Kirillov, was killed along with his deputy early Tuesday in an explosion in Moscow, Russia's Investigative Committee said.

Ukrainian security sources told CBS News the Security Service of Ukraine (SBU) killed Kirillov in a special operation. The claim couldn't be independently verified.

The sources said a scooter with explosives was detonated as Kirillov and his assistant were entering an apartment building.