The US military says two of its warships have sailed near islands claimed by China in the South China Sea, a move that has angered Beijing at a time of tense ties between the world's two biggest economies.
The busy waterway is one of a growing number of flashpoints in the US-China relationship, which also include a trade war, US sanctions and Taiwan.
President Donald Trump dramatically increased pressure on China to reach a trade deal by threatening to hike US tariffs on $US200 billion ($A285 billion) worth of Chinese goods this week and soon target hundreds of billions more.
The US guided-missile destroyers Preble and Chung Hoon travelled within 12 nautical miles of Gaven and Johnson Reefs in the Spratly Islands, a US military spokesman told Reuters.
Commander Clay Doss, a spokesman for the Seventh Fleet, said the "innocent passage" aimed "to challenge excessive maritime claims and preserve access to the waterways as governed by international law".
In Beijing, foreign ministry spokesman Geng Shuang said the US ships entered the waters near the islets without the Chinese government's permission, and the Chinese navy warned them to leave.
"The relevant moves by the US ships infringed upon Chinese sovereignty, and damaged the peace, security and good order of the relevant seas. China is strongly dissatisfied with this and resolutely opposed to it," he told a daily news briefing.
"China urges the United States to stop such provocative actions," Geng said, adding that China would continue to take the necessary steps to defend its sovereignty and security.
The operation was the latest attempt to counter what Washington sees as Beijing's efforts to limit freedom of navigation in the strategic waters, where Chinese, Japanese and some Southeast Asian navies operate.
China claims almost all of the strategic South China Sea and frequently lambasts the US and its allies over naval operations near Chinese-occupied islands.
Brunei, Indonesia, Malaysia, the Philippines, Taiwan and Vietnam have competing claims in the region.
China and the US have repeatedly traded barbs in the past over what Washington says is Beijing's militarisation of the South China Sea by building military installations on artificial islands and reefs.
China defends its construction as necessary for self-defence and says the United States is responsible for ratcheting up tension in the region by sending warships and military planes close to islands Beijing claims.
