The announcement by Moscow comes after the killing of a top Russian general last week.
The Federal Security Service (FSB) said in a statement carried by Russian news agencies that it had arrested four Russians accused of making preparations to kill senior Defence Ministry officials.
The FSB said the suspected organisers of the attacks were planning to kill one of the senior officers using a remotely controlled car bomb.
It said another senior official was to be assassinated by an explosive device hidden in an envelope.
The agency did not name the military officers being targeted.
The FSB released a video showing the arrest and interrogation of the suspects, who were not named.
The statement follows the death of Lieutenant General Igor Kirillov who was killed on December 17 by a bomb hidden on an electric scooter parked outside his apartment building as he left for his office in Moscow.
His assistant also died in the attack which was claimed by Ukraine and brought the conflict once again to the streets of the Russian capital.
The FSB has arrested a suspect, a citizen of the Central Asian nation of Uzbekistan, and claimed he said he had been recruited by Ukrainian special services.
Lt Gen Kirillov, 54, was the chief of Russia's Radiation, Biological and Chemical Protection Forces - special troops tasked with protecting the military from the enemy's use of nuclear, chemical or biological weapons and ensuring operations in a contaminated environment.
President Vladimir Putin described his killing as a "major blunder" by Russia's security agencies, noting they should learn from it and improve their efficiency.
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