The last US-Russia strategic nuclear arms control pact appeared on track to win a one-year extension, as Washington on Tuesday welcomed a proposal by Moscow for such an extension if both sides freeze all nuclear warhead deployments for that period.
The apparent breakthrough, coming after months of difficult talks and two weeks before the U.S. presidential election, appeared to narrow the gap between the sides over the fate of the 2010 New START agreement, which is due to expire in February.
The demise of the treaty would lift all remaining restraints on deployments of strategic nuclear warheads and the missiles and bombers that carry them, fueling a post-Cold War arms race between the world's largest nuclear weapons powers.
The United States last week rejected a Russian offer to unconditionally extend the pact for one year, saying that any proposal that did not envisage freezing all nuclear warheads - both strategic and tactical - was a "non-starter".
But a statement published by the Russian Foreign Ministry on Tuesday suggested that the two countries' positions had moved closer.
"Russia is proposing to extend New START by one year and is ready together with the United States to make a political commitment to 'freeze' the number of nuclear warheads held by the parties for this period," it said.
State Department spokeswoman Morgan Ortagus welcomed the Russian offer, saying in a statement that the United States appreciated Russia's "willingness to make progress on the issue of nuclear arms control."
"The United States is prepared to meet immediately to finalize a verifiable agreement. We expect Russia to empower its diplomats to do the same," she said.
Her statement highlighted one of a number of questions the sides would have to resolve to pave the way to a one-year New START extension: how they would verify that the other was adhering to the warhead deployment freeze.
The treaty can be extended for up to five years beyond its Feb. 5 expiration with the agreement of the U.S. and Russian presidents.
Extending the pact would mark a rare bright spot in the fraught relationship between the two countries. Failure to do so would remove the main pillar maintaining the nuclear balance between them and add yet another element of tension.
The Russian foreign ministry said the warhead freeze and one-year extension would be possible if Washington did not make any additional demands. It said the extension would give the two sides time to discuss nuclear arms control in greater depth.
Moscow and Washington have been at odds over the treaty - and other arms control issues - despite several months of talks. The United States has called for China to be included in a broader treaty that would replace New START.
But China, whose nuclear arsenal is much smaller than those of Russia and the United States, has rejected that proposal.
Last year the United States pulled out of a Cold War-era arms control pact banning ground-launched nuclear and conventional ballistic and cruise missiles with a range of between 310 and 3,400 miles (500-5,500 km), citing Russian violations denied by Moscow.