WASHINGTON DC: A Pentagon report for the first time has acknowledged that Russia is building and developing an "undersea" nuclear torpedo.

According to a report from the US Defense Department, which assesses the arms advancements being made in other countries, Russia is "developing" a "new intercontinental, nuclear-armed, nuclear-powered, undersea autonomous torpedo which is known in English as the Status-6 system, reported CNN.

Some analysts have branded it a "doomsday weapon."

According to the US officials, the Russian programme includes a drone-type device fired underwater with the potential of travelling thousands of miles and the capability of striking US targets along the coast, including military bases and cities. If activated, the intent would be widespread radioactive contamination.

The Defense Department, in its Nuclear Posture Review, noted that "Russia considers the United States and the North Atlantic Treaty Organization (NATO) to be the principal threats to its contemporary geopolitical ambitions."

"The Defense Intelligence Agency currently estimates Russia has a stockpile of 2,000 "non-strategic" nuclear weapons including short-range ballistic missiles, gravity bombs and depth charges that can go on medium range bomber aircraft," the report added.

The Pentagon maintained that the US had to balance the need for developing a plan for nuclear deterrence while at the same time maintaining a "commitment to nonproliferation and arms control," according to Deputy Defense Secretary Patrick Shanahan.

President Donald Trump issued a statement in support of the Defense Department efforts, claiming nuclear programs in other countries had grown in recent years.

"Over the past decade, despite United States efforts to reduce the roles and numbers of nuclear weapons, other nuclear nations grew their stockpiles, increased the prominence of nuclear weapons in their security strategies, and - in some cases - pursued the development of new nuclear capabilities to threaten other nations," the statement said.