Both India and China have tested weapons systems amid growing tension between the two countries.
China recently conducted a "very concerning" test of a hypersonic weapon system as part of its advance into space and military technologies, the top military official in the US said.
General Mark Milley, Chairman of the Joint Chiefs of Staff, was the first Pentagon official to confirm, on the record, the nature of the test by the Chinese military earlier this year.
Previously, the Financial Times reported the test involved a nuclear-capable hypersonic weapon that was launched into space, orbited the Earth and then re-entered the atmosphere and glided toward its target in China.
General Milley said he could not discuss details, due to aspects that involved classified intelligence.
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He did, however, say the US is also working on hypersonic weapons, but has not conducted a test of the sort China had achieved.
"What we saw was a very significant event of a test of a hypersonic weapon system, and it is very concerning," Milley said in an interview.
"I think I saw in some of the newspapers, they used the term Sputnik moment," he added.
"I don't know if it's quite a Sputnik moment, but I think it's very close to that."
Meanwhile, India has also undertaken its own weapons test amid rising border tensions with China.
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India test-fired a nuclear-capable intercontinental ballistic missile, with a range of 5,000km from an island off its east coast.
The launch was in line with "India's policy to have credible minimum deterrence that underpins the commitment to no first use", a government statement said.
The statement also said the Agni-5 missile splashed down in the Bay of Bengal with "a very high degree of accuracy".
Beijing's powerful missile arsenal has driven New Delhi to improve its weapons systems in recent years, with the Agni-5 believed to be able to strike nearly all of China.
It has been developing its medium and long-range nuclear and missile systems since the 1990s amid increasing strategic competition with China.
Tension between them flared last year over a long-disputed section of their border in the mountainous Ladakh area.
India is also increasingly suspicious of Beijing's efforts to heighten its influence in the Indian Ocean.