Russia has used oil revenues to steadily increase the pace of its military modernization over the past couple of years, said Gates, who visited Moscow last week.

"But I would point out that we're coming from a very low base," he told reporters. "In the 1990s, the Russian military was almost inert. And they're spending, perhaps, 10 percent of what we spend, if that, on defense."

"So I think what you see is that these kinds of things that he's talking about are basically an assertion that Russia is back and intends to play a major role on the world stage and intends to be taken seriously," he said.

Asked whether Putin's comments alarmed him, Gates said, "No, it doesn't alarm me."

Putin made the remarks in a a video link-up with servicemen at the Plesetsk nuclear missile base.

He said Russia would build another nuclear submarine next year and was also planning a "completely new" atomic weapon.

"We have grandiose plans and they are absolutely realistic," Putin said, speaking hours after the military announced the successful test firing of a Topol intercontinental ballistic missile.