The Kremlin admitted Wednesday that Russian television had accidentally shown secret plans detailing a nuclear torpedo system in development.

Two Kremlin-controlled channels, NTV and Channel One, showed a military official looking at a confidential document containing drawings and details of a weapons system called Status-6, designed by Rubin, a nuclear submarine construction company based in Saint Petersburg.

The nuclear torpedoes, to be fired by submarines, would create "zones of extensive radioactive contamination making them unsuitable for military or economic activity for a long period," says the document, which is clearly visible in the footage for several seconds.

The images were filmed during a meeting of President Vladimir Putin with military officials in the Black Sea city of Sochi on Monday.

The footage aired on Tuesday and was later deleted by the channels, but several websites still published screenshots from it.

"It's true some secret data got into the shot, therefore it was subsequently deleted," Putin's spokesman Dmitry Peskov told journalists.

"In future we will undoubtedly take preventive measures so this does not happen again."

It remained unclear how the images ended up being broadcast on the tightly-controlled channels.

The document was shown at a meeting where Putin warned that "Russia will take necessary retaliatory measures to strengthen the potential of our strategic nuclear forces."