They will try to reach a trade deal before a March 1 deadline after which the U.S. has threatened to increase tariffs on US$200 billion worth of Chinese imports and risk retaliatory action from China.
The two warships entered China's territorial seas around the Nansha Islands without permission from the Chinese government, ministry spokeswoman Hua Chunying said at a daily news briefing.
Two Arleigh Burke-class destroyers - the USS Spruance and the USS Preble - conducted a freedom-of-navigation operation on Monday, sailing within 12 nautical miles of Chinese outposts in the contested Spratly Islands.
The Chinese side immediately conducted verification and identification on the US ships and warned them to leave, said the spokeswoman.
11, the United States conducted another Freedom of Navigation Operation (FONOP) in the South China Sea, sending two naval vessels near the Spratly Islands.
Beijing accused the United States of entering Chinese waters without permission and engaging in provocations that threaten China's sovereignty.
The US is "determined to stir up trouble in the South China Sea, create tension and undermine peace", Hua said.More news: How to watch Monday coverage of AT&T Pebble Beach Pro
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China firmly opposed the relevant action and urged the U.S.to immediately stop its provocations, Hua stressed.
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 South-east Asian navies operate.
China's foreign ministry expressed anger on Monday after the warships sailed in the disputed South China Sea. In January, the destroyer USS McCampbell challenged China's claims to the Paracel Islands.
Speaking on background, a US official said the Navy ships passed near Mischief Reef, which China has augmented with a huge land reclamation project and equipped with missiles, extensive surveillance equipment, and a military-grade airfield, even though the reef is also claimed by Taiwan, Vietnam, and the Philippines. China has built and militarized artificial islands in the sea in a bid to maintain its control.
Communist superpower China claims ownership over nearly all of the South China Sea - frequently slamming the United States and its allies for naval operations in the territory.
Tensions have been high for years between Washington and Beijing in the South China Sea, with the USA regularly drawing Chinese ire.
Fears have grown in recent months that the US-China trade dispute is just one element in a bilateral relationship that is fast cooling across the board, with top US administration officials sharply criticising Beijing for everything from human rights abuses to cyber espionage in the US.