NATO Urges ‘Restraint’ As Last US-Russia Nuclear Treaty Expires

"Restraint and responsibility in the nuclear domain is crucial to global security," an official from the military alliance said, on condition of anonymity.

New START, signed during a warmer period of relations, ended Thursday, with President Donald Trump not following up on Russian counterpart Vladimir Putin's proposal to extend the treaty's limits for one year.

U.N. Secretary-General Antonio Guterres called it a "grave moment for international peace and security" and urged Washington and Moscow to head quickly to the negotiating table.

"For the first time in more than half a century, we face a world without any binding limits on the strategic nuclear arsenals of the Russian Federation and the United States of America," Guterres said in a statement. 

The NATO official said Russia and China were both ramping up their nuclear capabilities and that the alliance "will continue to take steps necessary" to ensure its own defenses.

"Russia's irresponsible nuclear rhetoric and coercive nuclear signaling demonstrate a posture of strategic intimidation," the official said. 

Meanwhile, "China continues to rapidly expand and diversify its nuclear arsenal with more warheads and a larger number of sophisticated delivery systems," they added.

The Kremlin Thursday said it regretted the end of the treaty and called it a negative step.

"We view it negatively. We express our regret in this regard," Kremlin spokesman Dmitry Peskov told reporters.

Washington has said any new nuclear agreement would have to include China, but international efforts to encourage Beijing to join fresh talks have so far failed.

"China's nuclear capabilities are of a totally different scale as those of the United States and Russia," Foreign Ministry spokesman Lin Jian told a news conference Thursday.

Beijing "will not participate in nuclear disarmament negotiations at this stage," he said.

Trump has frequently lashed out at international limits on the United States and called for nuclear testing to resume after a long moratorium, although he has not followed up.

But some observers say the expiration of New START owes less to ideology than to the workings of the Trump administration, where career diplomats are sidelined, simply not having the bandwidth to negotiate a complex agreement.

China's nuclear arsenal is growing quickly with an estimated 550 strategic nuclear launchers, which is still well below the 800 each of Russia and the United States capped under New START. France and Britain, treaty-bound U.S. allies, together have another 100.

Daryl Kimball, executive director of the Arms Control Association, which warns of nuclear risks, agreed that China should engage on its nuclear program but wondered if Trump has even tried.

He said that Trump and Putin could agree to keep current limits and then press China.