"We do not perceive Russia's nuclear sustainment and modernization activities as threatening, and what they are doing is fully consistent with our mutual obligations under the Moscow Treaty," deputy spokesman Adam Ereli told reporters.

"Our mutual obligations in this area are covered under the Moscow Treaty. Pursuant to that treaty, we have regular consultations" with Moscow, Ereli said.

"And based on those regular consultations, we are confident that Russia's plans are not threatening and are consistent with its obligations, and I think are indicative of a new strategic relationship between the United States and Russia that is focused on reducing threats and increasing confidence," he added.

Putin announced in Moscow on Wednesday that Russia would soon be armed with nuclear weapons systems "which do not exist and are unlikely to exist in other nuclear powers."

"We have not only conducted tests of the latest nuclear rocket systems," Putin told a meeting of the armed forces' leadership. "I am sure that, in the coming years, we will deploy them."

The ITAR-TASS news agency speculated that Putin was referring to the mobile Topol-M missile, which is analogous to the US Minuteman-3 missile and is meant to form the backbone of Russia's future strategic nuclear arsenal.

Russia this year also successfully test-fired a different new missile that its developers claim can penetrate any shield, since it flies in space on a ballistic trajectory and in the atmosphere as a cruise missile -- swerving away from interceptor rockets.