"They (China) have an obligation to negotiate in good faith with us and the Russians," American envoy to the negotiations Marshall Billingslea told reporters.

"They stood up not just the United States and Russia but they stood up the entire world," he said.

On Monday American and Russia delegations met in Vienna to discuss the New START treaty, which limits each side to 1,550 deployed nuclear warheads but which is due to run out in February.

US President Donald Trump has insisted China should be involved in discussions to extend the treaty, but Beijing has shown no interest in taking part.

Billingslea said another round of talks could take place towards the end of July but admitted it could once again be restricted to Washington and Moscow and didn't rule out an extension of the bilateral accord.

"The Russian Federation did not agree with my request to pressure China to join as a responsible party into these talks, but they also... are not opposed to China joining," Billingslea said.

He added that he hoped more international pressure would come to bear on Beijing.

However, on Tuesday the Russian envoy to the talks Deputy Foreign Minister Sergei Ryabkov said it was "unrealistic to count on China's participation".