The United States has expressed concern over Russia's development of a new state-of-the-art offensive weapon—a fast, nuclear-armed submarine drone—that could penetrate America's defensive shield and deliver a nuclear payload that could devastate American cities in case of an armed conflict between the two powers.

During a joint hearing of the House Armed Services and House Foreign Affairs Committees, US Department of State Undersecretary Rose Gottemoeller sounded the alarm on Russia's new weapon.

"I know we are concerned about it; of course we are concerned about it as threat to the United States," Gottemoeller said under questioning from Rep. Mike Turner, as quoted by The Free Beacon.

The senior state official, who is the key policymaker for arms control issues, further warned that the new Russian weapon would be a greater threat to the U.S. if "widely put into operation."

Upon hearing this, Turner remarked: "One would probably be sufficiently troubling."

"I think it is a troubling system, sir," Gottemoeller said.

The lawmaker also asked the State Department official how the U.S. has conveyed its concern to Moscow over its new offensive weapon.

Gottemoeller said she has already raised the matter with Russian officials, but refused to give further details.

She nevertheless assured Congress members that the discussions "make it clear to them that it is a concern of the United States of America."

Early last month, a television station controlled by the Russian government aired a supposedly classified document revealing the drone submarine as a nuclear-armed, nuclear powered unmanned underwater vehicle.

The document supposedly detailed just how powerful the Russian underwater drone called "Status 6" is. It can reportedly travel thousands of miles at high speeds, making it potent to be utilised for nuclear attacks on U.S. coastal cities.

The North Atlantic Treaty Organisation (NATO) has already given a code name for the drone: "Kanyon." Intelligence experts believe this weapon can mount a powerful multi-megaton nuclear warhead for use against U.S. harbours and coastal cities.