Russia said on Thursday it regretted the expiry of its last remaining nuclear arms treaty with the United States but was still ready to talk, according to Reuters.
Axios reported that negotiations had been taking place over the past 24 hours in Abu Dhabi and the two countries were closing in on a deal to keep observing key terms of the New START treaty, which limits each side's numbers of missiles, launchers and strategic nuclear warheads.
US President Donald Trump has not formally responded to a proposal from Russian President Vladimir Putin to stick to those central provisions for one more year, even though there is no legal option to extend the full treaty.
Kremlin spokesman Dmitry Peskov said Russia was still ready to engage in dialogue with the US if Washington responded constructively to Putin's proposal.
"Listen, if there are any constructive replies, of course we will conduct a dialogue," Peskov told reporters.
New START was the last in a series of nuclear agreements between Moscow and Washington dating back more than half a century to the Cold War.
Besides setting numerical limits on weapons, they included inspection regimes that experts say served to build a level of trust and confidence between the nuclear adversaries, helping make the world safer.
If nothing replaces the treaty, security analysts see a more dangerous environment with a higher risk of miscalculation.
Forced to rely on worst-case assumptions about the other's intentions, the US and Russia would see an incentive to increase their arsenals, especially as China plays catch-up with its own rapid nuclear build-up.
Trump has said he wants to replace New START with a better deal, bringing in China but Beijing has declined negotiations with Moscow and Washington. It has a fraction of their warhead numbers - an estimated 600, compared to around 4,000 each for Russia and the US.
Repeating that position on Thursday, China said the expiration of the treaty was regrettable, and urged the US to resume dialogue with Russia on "strategic stability".