Russia is to deploy new missiles in a Baltic enclave near Nato member Poland, Russian President Dmitry Medvedev says.
Short-range Iskander missiles in the Kaliningrad region would "neutralise" the planned US anti-missile shield in Poland and the Czech Republic, he said.
The US says its shield is a defence against missiles from "rogue" nations, but Moscow sees it as a direct threat.
Mr Medvedev also said he wanted to extend Russia's presidential term to six years from the current four.
He did not explain if he wanted to extend his own term, or change the rules for his successor.
There has long been speculation that Mr Medvedev is a stop-gap so that Prime Minister Putin - who served the maximum two consecutive terms - can return to the top job, correspondents say.
'Conceited' US policy
In his first state-of-the nation address, Mr Medvedev said Moscow would deploy the Iskander missile system in the Kaliningrad region - between Nato members Lithuania and Poland - to "neutralise - if necessary - the [US] anti-missile system".
"Naturally, we also consider using for the same purpose the resources of Russia's navy," he said.
Mr Medvedev also said Russia would jam the US anti-missile system electronically.
Mr Medvedev's announcement is extremely provocative, but the Kremlin's clear message is that America is to blame, the BBC's Rupert Wingfield-Hayes in Moscow says.
Lithuanian President Valdas Adamkus later said that Russia's decision to deploy missiles was "beyond comprehension".
In his speech to lawmakers, the Russian leader also said the August war in Georgia had resulted from a "conceited" US foreign policy.
He said "the conflict in the Caucasus was used as a pretext for sending Nato warships to the Black Sea and also for the foisting on Europe of America's anti-missile systems".
Mr Medvedev, who succeeded Vladimir Putin in May, vowed that Russia "won't retreat in the Caucasus".
Mr Medvedev also blamed Washington for the global financial crisis, but said Russia would "overcome" the challenge.