Washington (CNN) The Trump administration will soon start nuclear negotiations with Russia, US national security adviser Robert O'Brien said Wednesday, speaking exactly one year before the last remaining US nuclear arms pact with Moscow is set to expire.

"We are going to confront the Russians where we need to, but at the same time I think we'll negotiate, we'll start negotiations soon on arms control, on the nuclear issue which is, you know, important to the safety of the world, not just the US and Russia," O'Brien said in a speech at the at the Meridian International Center in Washington to ambassadors from around the world.

O'Brien spoke as the US and Russia hit the one-year deadline to extend the New START Treaty, the last legally binding agreement limiting their nuclear arsenals -- the world's largest. For arms control experts who stress that nuclear diplomacy takes time, the delay in launching significant talks has raised concerns about the Trump administration's interest in remaining in the treaty or, more broadly, in adhering to the limits of arms control pacts at all.

A potential poison pill

They point to President Donald Trump's past criticism of New START as a "bad deal" and the role of former national security adviser John Bolton -- a longstanding critic of arms control agreements that he believed constrained American power. They flag the administration's pattern of rejecting international agreements, including two other nuclear pacts, the Intermediate Range Forces Treaty and the Iran nuclear deal.

Renewing New START would be a simple bureaucratic step that Russian officials have stressed they are ready to take, but Trump and administration officials have suggested that they are interested in negotiating a new pact that includes China and perhaps other countries instead.

While administration officials say the President is simply interested in overhauling an out of date treaty, some arms control experts see the suggestion of adding China as a poison pill. With a much smaller nuclear arsenal than either Moscow or Washington, Beijing has little incentive to sign on to a pact that curbs its arsenal at levels far below its chief geopolitical rivals.

New START treaty limits both nations to deploying 1,550 nuclear warheads over 700 delivery systems, including intercontinental ballistic missiles, submarine-launched ballistic missiles, and bombers. It also allows for 18 on-site inspections every year that allow each side to keep a close eye on the others' capabilities.

The treaty is set to expire in 2021 but could be extended for up to five years if both sides agree.

The cost of failing to extend New START will be a large step backward, said Richard Burt, former US ambassador to Germany and the chief negotiator of START-I, a predecessor treaty to New START.

"The US and Russia hold over 90% of the world's nuclear arsenals," Burt said. If the New START Treaty is allowed to expire, "then we're living in a world where there's no longer any real transparency or predictability in the US -- Russia nuclear competition, there will be no more guard rails in the nuclear arms race and we will be back where we were, way back in the 1960s, because ... they will be gone."

In April, Secretary of State Mike Pompeo told lawmakers that the US was at the "very beginning of conversations about renewing" the treaty. O'Brien's comments 10 months later suggest the talks still have not launched seriously.

"History suggests new negotiations will take time, so it's important to get started on defining the parameters of a new negotiation while preserving the security benefits for the American people of maintaining New START in place," said Lynn Rusten, a vice president at the Nuclear Threat Initiative.

O'Brien noted in his remarks that Russia is "an important country ... because, you know, they have over 1,400 nuclear missiles, many with multiple range vehicles on them and they are modern. President [Vladimir] Putin has put a lot of money into his military over the past several years to re-assert Russian power."

The US has also been modernizing its military. The Pentagon announced Tuesday that it had deployed a new submarine-launched low-yield nuclear weapon , something it sees as critical to countering the threat posed by Russia's arsenal of smaller tactical nukes.

Several former high-ranking administration officials, however, have said the weapons increase the potential for nuclear conflict.

The ball is in America's court

Russia's foreign minister, Sergei Lavrov, said during a December visit to Washington that Putin has emphasized "Russia's preparedness to right now agree on [New START's] extension in order to alleviate the tension for global community, considering that the last instrument of arms control between the US and the Russian Federation will be -- well, not destroyed, but it will just not be in force anymore. And we are prepared to do that even today, and the ball is in our American partner's court."

Asked at the same State Department press conference if the US would be open to renewing New START without the Chinese, Pompeo didn't say an outright "no," but made clear that's not what the administration wants.

"As weapon systems move and advance, as new countries develop these capabilities, there is real risk that there is a reduction in strategic stability just staying right we are today so that it -- the reason that we're asking for other countries to participate -- and Foreign Minister Lavrov suggested France and the United Kingdom join as well, happy to consider that too, the cumulative mission set has to be global strategic stability, and we will continue to engage in conversations with the Russians and others with the aim of achieving that," Pompeo said.

Rusten, a former arms control and non-proliferation official who has served at the White House and State Department, was among several arms control experts who said that since the US has also been working to modernize its nuclear arsenal, the best approach would be to "extend New START now and jointly announce US-Russian principles to guide negotiation of a future agreement to build on the foundation of New START and further reduce and address additional categories of nuclear weapons."