(CNN)Russian police are investigating a break-in at a top-secret airborne nuclear command center, nicknamed the "doomsday plane."
The Ilyushin-80 aircraft is designed to carry top officials, including President Vladimir Putin, in the event of a nuclear attack.
The crime was only uncovered during an inspection of the aircraft at Beriev Taganrog Aviation Scientific and Technical Complex, officials revealed Monday.
A cargo hatch was found to have been opened and 39 pieces of radio equipment were reported as missing from inside the aircraft. The suspects have not been identified.
Security has now been stepped up at the site, according to the Kremlin, which is investigating the incident. Few details of the aircraft are available, as the plane and its contents are a state secret.
Dmitry Peskov, Putin's press secretary, described the episode as an "emergency situation" in a conference call with journalists and said: "Of course, there will be an investigation, and measures will be taken so that this does not happen again."
Peskov did not specify who is responsible for the aircraft's security.
The plane had been undergoing routine maintenance to its landing gear rods before the theft, Russian news agency Tass reported, and all equipment was in place at that time.
Airborne Command Posts were first nicknamed doomsday planes by the United States, as they are designed for use in the event of nuclear war or a major disaster that would see ground-based command infrastructure destroyed.
The most famous models of such specialized aircraft are the US Boeing E-4B, based on th