GENEVA - The United States urged China on Tuesday to join trilateral nuclear arms talks with Moscow, calling Beijing's secrecy around growing stockpiles a "serious threat to strategic stability."US President Donald Trump said last year he had discussed a new accord on limiting nuclear arms with Russian President Vladimir Putin and hoped to extend that to China in what would be a major deal between the globe's top three atomic powers. But China has so far refused to take part."We think, given the fact that China's nuclear stockpile is estimated to double over the next ten years, now is the time to have that trilateral discussion," Robert Wood, US disarmament ambassador, told reporters on the opening day of the UN-backed Conference on Disarmament in Geneva.He said that Washington had discussed the potential trilateral talks in a security meeting with Russia last week and had reached an "understanding" about pursuing them. "We cannot afford to wait," he added.Asked how to go about pressuring Beijing to join, Wood said that he hoped Russia, and others, would help. "Hopefully over time and through the influence of others besides the United States, they (China) will come to the table. We think it's imperative for global security that the Chinese do that."Russian Foreign Minister Sergei Lavrov said last week that Russia would take part in potential trilateral talks but that he "won't force China to change" its current position.China has previously said its weapons were the "lowest level" of its national security needs and not comparable to those of Russia and the United States.The United Nations is seeking the total elimination of nuclear arms but talks have been deadlocked for more than 20 years.Other talks between the five declared nuclear powers that have ratified the 1970 Non-Proliferation Treaty (NPT) - China, United States, Russia, France and the United Kingdom - are ongoing and a meeting is planned in London next month.However, Wood said this was not the right framework for nuclear arms talks with Beijing.In his speech, China's disarmament Ambassador Li Song did not refer to its own nuclear stockpiles but called for cooperation among nuclear powers and made a thinly-veiled swipe at the Trump administration.Li called for a commitment to multilateralism, "with no exceptions, least of all the big power which shoulders a special responsibility for international peace and security and who is not expected to play the role of a 'spoiler' to our collective efforts and to withdraw from treaties."