The threat of a renewed global nuclear arms race came a little closer to reality as the last remaining nuclear arms control treaty between the United States and Russia expired at midnight GMT on Thursday.

The New START pact and its predecessors had for decades imposed limits on the world's two largest nuclear arsenals.

It lapsed at midnight GMT or 7 p.m. EST, according to the United Nations, without an agreement to extend it.

The US and Russia, the world's two largest nuclear powers, will now no longer be bound by upper limits for their strategic nuclear arsenals.

Russia, however, pledged to act responsibly while warning it would take "decisive" measures if its security were threatened, the Foreign Ministry in Moscow said on Wednesday.

Washington has not announced plans to adhere to the treaty's limits beyond the deadline.

Trump insists arms control deal needs to include China

New Strategic Arms Reduction Treaty (START), signed in 2010, capped both the US and Russia at 1,550 deployed strategic nuclear warheads.

Last year, Russian President Vladimir Putin had floated the proposal for a one-year extension. In October, US President Donald Trump said that sounded "like a good idea," but there were no subsequent negotiations.

Trump has insisted that he wants any future arms control agreement to include China, an idea Beijing rejects and Moscow considers unnecessary.

In a video call with Chinese President Xi Jinping, Putin discussed the expiration of the nuclear arms treaty and reiterated Moscow's commitment to "act in a balanced and responsible manner" while remaining "open to searching for ways of negotiations to ensure strategic stability," according to the Kremlin.

Meanwhile, US Secretary of State Marco Rubio said on Wednesday that Trump would decide on the treaty later, but added that "it's impossible to do something that doesn't include China, because of their vast and rapidly growing stockpile."

On Thursday, German Foreign Minister Johann Wadephul also called on China to show "restraint" in weapons development while saying future arms control efforts need to include Beijing.

'High risk of nuclear weapon usage'

UN Secretary-General Antonio Guterres on Wednesday rang the alarm bells over the treaty's expiration, calling it a "grave moment for international peace and security." He implored both countries to return to negotiations without delay at a time when "the risk of a nuclear weapon being used is the highest in decades."

Earlier, Pope Leo XIV also called for the de-escalation from a new arms race and said during his weekly general audience, "I urge you not to abandon this instrument without seeking to ensure that it is followed up in a concrete and effective manner."

Edited by: Sean Sinico