Russian Prime Minister Vladimir Putin has warned that Washington's designs to build a weapons defense system could strain talks between the United States and Russia on replacing the Strategic Arms Reduction Treaty.

Putin warned that Washington's designs threatened to offset the Cold War balance of power, advising instead that Russia develop offensive strike systems to counter the missile shield.

"If we don't develop a missile defense system, a danger arises for us that with an umbrella protecting our partners from offensive weapons, they will feel completely safe," Putin told reporters during a working visit to the Russian far eastern city Vladivostok.

"The balance will be disrupted, and then they will do whatever they want, and aggressiveness will immediately arise both in real politics and economics," he cautioned.

The remarks from Russia's most powerful politician signaled the difficulties facing talks on a replacement of the 1991 Strategic Arms Reduction Treaty, otherwise known by its acronym START. The remarks also reflect lingering unease at Washington's defense shield plan despite statements by U.S. President Barack Obama earlier this year that the United States would scrap parts of George W. Bush's missile defense plan.

The arms treaty expired in early December, and both the United States and Russia are hammering out details of a new deal that would reduce the number of nuclear arms by at least one-quarter on both sides.

As an alternative to the development of offensive weapons, Putin said Washington could afford greater details of its missile plan, allowing Russia to exchange data on its own weapons program.

American officials have repeatedly refuse to link START talks to the missile defense plan, which is predominantly geared towards shielding threats from Iran or North Korea and not Russia.

Last week Russia President Dmitry Medvedev reiterated that Russia would continue to develop strategic offensive missiles after the signing of the new START treaty, expected in the next few months.

"This is normal," he told a television address. "The whole world is doing this. Of course, this work needs to take place within the framework of conventions and agreements, including our future agreements with the Americans.

"But this process will continue and our nuclear shield will always be effective and sufficient for protecting our national interest," Medvedev said.

Senior administration officials in Washington have been swift and keen to rebuff any attempt to broaden START negotiations to cover defensive weapons systems.

Obama and Medvedev failed to clinch final agreement on START during a recent meeting on the sidelines of the U.N. climate conference in Copenhagen, Denmark. No reason was given for that failure, but officials from both sides conceded that talks were nearing conclusion.