The US's first test of a missile since withdrawing from the Intermediate-Range Nuclear Forces Treaty has Russia and China on edge, as both rivals contend that the US is starting a new arms race that raises the possibility of armed conflict.

On Sunday, the US tested its first ground-launched cruise missile since the INF Treaty collapsed earlier this month.

Russia said the US had "set the course for fomenting military tensions," and China expressed concerns that the US would "trigger a new round of arms race."

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The US's first test of a missile since withdrawing from the Intermediate-Range Nuclear Forces Treaty has Russia and China rattled, with each nuclear-armed rival warning that the US is igniting a great-power arms race.

As Russia said the US had "set the course for fomenting military tensions," China expressed concerns that American actions would "trigger a new round of arms race," making conflict more likely.

Arms-control experts have said that a "new missile race" is underway, arguing that strategic rivals are likely to match US weapons developments "missile for missile."

The US military on Sunday conducted its first flight test of a conventional ground-launched cruise missile that would have been banned under the INF Treaty a little over two weeks ago.

Read more: The US fired off a previously banned missile, the first since the collapse of a Cold War-era nuclear-arms pact with Russia

The 1987 treaty was a Cold War-era agreement between Washington and Moscow that put restrictions on missile development, prohibiting either side from developing or fielding intermediate-range ground-launched missiles, systems with ranges of 500 to 5,500 kilometers. China — never a party to this pact — has been developing missiles in this range for decades.

Accusing Russia of violating the agreement through its work on the Novator 9M729, a missile that NATO refers to as SSC-8, the US said earlier this year that it would "move forward with developing our own military response," a position supported by NATO.

When the US formally withdrew from the treaty at the start of August, Secretary of Defense Mark Esper explained that the Department of Defense would "fully pursue the development of these ground-launched conventional missiles."

Sixteen days later, the US tested its first post-INF missile — alarming not only Moscow but Beijing.

On Sunday at 2:30 p.m. PT, the Defense Department conducted a flight test of a conventionally configured ground-launched cruise missile at San Nicolas Island, California. DoD photo by Scott Howe

"We will not allow ourselves to get drawn into a costly arms race," Russia's deputy foreign minister, Sergei Ryabkov, told Russian state media, according to The Guardian.

Urging the US to let go of a Cold War mentality, a spokesman for China's Ministry of Foreign Affairs, Geng Shuang, said that the US test and future tests would ultimately "lead to escalated military confrontation" that would harm "international and regional security."

Russia, which insists it did not violate the INF Treaty, has repeatedly warned the US against deploying intermediate-range missiles in Europe.

The weapon tested Sunday, as The War Zone explains, was a ground-launched BGM-109 Tomahawk, a variant of the BGM-109G Gryphon, a US missile system that together with the Pershing II mid-range ballistic missile comprised the forward-deployed tactical nuclear forces in Europe before the INF Treaty was signed and all relevant weapon systems were destroyed.

In an apparent response to Moscow, the US said it had no plans to put post-INF Treaty missiles in Europe. Beijing may actually have more reason to worry.

The Pentagon — and specifically the new secretary of defense — has expressed an interest in positioning new intermediate-range missiles in the Pacific to counter regional threats like China.

Esper told reporters recently that at least 80% of China's inventory "is intermediate-range systems," adding that it shouldn't surprise China "that we would want to have a like capability."

China did not respond positively to the news, saying it wouldn't let the US put missiles on its "doorstep."

The US has not announced where any of these missiles would be deployed.

Read more: China warns it will not 'sit idly by' while the US moves to put new strike missiles on its 'doorstep'

While some observers see the US wading into a major arms race as it focuses more on great-power competition, others see this as a reasonable strategic evolution in US military capabilities.

"We want China's leadership to wake up every morning and think 'This is not a good day to pick a fight with the United States or its allies,'" Tom Karako, a missile-defense expert at the Center for Strategic and International Studies, told Insider.

Over the years, China has developed increasingly capable missiles designed to target US bases across the Pacific and sink US carriers at sea, while the US has expressed an interest in deploying new capabilities to tilt the scales back the other way.