US President Barack Obama on Wednesday enlisted retired general and former secretary of state Colin Powell to press his fellow Republicans to ratify a landmark arms control treaty with Russia.

"I fully support this treaty and I hope that the Senate gives its advice and consent for the ratification of the treaty as soon as possible," Powell said during a brief joint public appearance with Obama at the White House.

His message came as Russian Prime Minister Vladimir Putin warned in an interview with CNN television to be broadcast Wednesday that Moscow would likely build up its arsenal if the accord fails.

Powell, a veteran of 25 years of nuclear arms control pacts between Moscow and Washington, stressed "the world has benefited by having fewer of these horrible weapons in existence, and we hope that we can continue this process."

The popular retired general's comments came as his fellow Republicans in the US Senate blocked action on the new Strategic Arms Reduction Treaty (START), which Obama wants ratified by the end of the year.

Taking aim at their stated concerns, Powell said the treaty included verification mechanisms that were "more than adequate to make sure that we know what they are doing and they know what we are doing."

Echoing the message of every top uniformed official at the Pentagon, he denied that US missile defense plans were in any way constrained by the accord, and praised Obama's plans for modernizing the nuclear arsenal.

Number-two Senate Republican Jon Kyl has pledged to block action on the accord this year, citing modernization worries.

The White House plans to spend 85 billion dollars over ten years to refurbish US atomic weapons.

The 100-seat Senate currently counts 56 Democrats and two independents who vote with them, and ratification requires 67 votes. Republicans hold 42 seats now but that number will rise to 47 when a new Congress arrives in January.

The agreement, a key part of Obama's efforts to "reset" relations with Moscow, restricts each nation to a maximum of 1,550 deployed warheads, a cut of about 30 percent from a limit set in 2002, and 800 launchers and bombers.

The agreement, which has broad US public support, would also return US inspectors who have been unable to monitor Russia's arsenal since the agreement's predecessor lapsed in December 2009.

The Russian lower house of parliament, the State Duma, has indicated it will ratify the treaty only after its ratification by the US Senate.

Putin insisted that his warning was "not a threat," according to excerpts of the interview released by CNN.

"We've been simply saying that this is what all of us expects to happen if we don't agree on a joint effort there," said Putin, who warned scuttling the agreement would be "very dumb."

In an effort to quiet Republican objections, Senate Foreign Relations Committee Chairman John Kerry, a Democrat, released letters from the heads of the three primary US nuclear weapons laboratories declaring their support for the Obama's modernization plans.

"The directors' strong support is a crystal clear affirmation that we are doing precisely what is needed to maintain a nuclear deterrent that is second-to-none," Kerry said in a statement.

"There are no legitimate excuses for delay and this is far too important to succumb to raw politics. We owe our country no less than to act now," he added.

In their letter, the lab chiefs said Obama's funding plan would meet their needs "for ensuring a safe, secure, reliable and effective stockpile."

"The proposed budgets provide adequate support to sustain the safety, security, reliability and effectiveness of America's nuclear deterrent" within the treaty's limits, "with adequate confidence and acceptable risk," they wrote.