Geneva, Switzerland - President Donald Trump's administration on Friday urged three-way talks with Russia and China to set new limits on nuclear weapons, after the last treaty between Washington and Moscow expired.

Thomas DiNanno, the undersecretary of state for arms control, told the UN Conference on Disarmament that the lapsed New START treaty had "fundamental flaws."

"Serial Russian violations, growth of more worldwide stockpiles and flaws in New START's design and implementation gives the United States a clear imperative to call for a new architecture that addresses the threats of today, not those of a bygone era," he told the conference at the United Nations' European headquarters in Geneva.

"As we sit here today, China's entire nuclear arsenal has no limits, no transparency, no declarations, had no controls," he lamented.

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He added that "the next era of arms control can and should continue with clear focus, but it will require the participation of more than just Russia at the negotiating table."

The expiration of New START, which restricted the US and Russia to deploying 1,550 nuclear warheads each, marks the first time in decades that the world finds itself without a treaty to curb the positioning of the planet's most destructive weapons, sparking fears of a fresh arms race.

President Donald Trump did not accept a proposal from Russian counterpart Vladimir Putin to keep New START's restrictions in place for another year, and called Thursday for a "new, improved and modernized treaty."

"New START does not allow the United States to credibly uphold both our strategic deterrence commitments to the American people and our extended deterrence commitments to our allies," DiNanno insisted.

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"We aim to improve upon New START in order to achieve a new, better strategic stability and arms control architecture that makes the world safer and more secure," he said.

China has already publicly rejected joining disarmament negotiations, noting that its arsenal is much smaller, although it is rapidly growing.

China's ambassador Shen Jian reiterated that position on Friday, insisting to the disarmament body that "China's nuclear capabilities are nowhere near the level of those of the US or Russia".

"China would not participate in nuclear disarmament negotiations at this stage," he said.

Russia's ambassador Gennady Gatilov meanwhile insisted that any new nuclear talks should also include other nuclear-armed states such as France and Britain.