"The United States has not moved away from its position of including China. From our side, we have explained in detail why we consider it unrealistic to count on China's participation," Deputy Foreign Minister Sergei Ryabkov, Russia's negotiator in the talks, was quoted as saying by news agency RIA Novosti.

"And we will not use our influence on China as the Americans want," he added.

US President Donald Trump has insisted China should be involved in discussions to extend New START, the treaty that limits US and Russian nuclear warheads, because he says Beijing has had a free pass to develop weapon systems.

And the US envoy to the talks, Marshall Billingslea, insisted on Tuesday that China had "an obligation to negotiate in good faith with us and the Russians".

The talks on extending the treaty -- which expires in February 2021 and limits each side to 1,550 deployed nuclear warheads -- took place in Vienna on Monday, with Billingslea saying they had been "very positive".

China has shown no interest in taking part and analysts say there is little prospect of an imminent agreement between Russia and the United States.

Shortly before talks began, Billingslea again raised the issue of what he called China's "no-show" by tweeting a picture of an empty negotiating table decked with Chinese flags.

China's mission in Vienna responded by ridiculing the tweet as "performance art".