USA warships again challenge China's claims in South China Sea

The two sides are trying to hammer out a deal ahead of the March 1 deadline when U.S. tariffs on US$200 billion worth of Chinese imports are scheduled to increase to 25 percent from 10 per cent.

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.

The alleged incursion by two US warships into the internationally disputed waters of the South China Sea was the second such move within five weeks.

China and the U.S. 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. The archipelago lies off the coasts of the Philippines, Malaysia, and southern Vietnam.

Pentagon officials said two guided-missile destroyers had travelled within 12 nautical miles of Mischief Reef in the fiercely disputed Spratly Islands.

Speaking at a meeting of the Atlantic Council in Washington last week, Admiral John Richardson, chief of US Naval Operation, called for firmer rules governing naval encounters in disputed waters such as the South China Sea.

"All operations are designed in accordance with global law and demonstrate that the United States will fly, sail and operate wherever worldwide law allows", Doss said, adding "that is true in the South China Sea as in other places around the globe".

She demanded the United States "immediately stop its provocative actions" after the two U.S. guided-missile destroyers conducted what Washington called "freedom of navigation" exercises in the area.

"The relevant actions of the U.S. warships violated Chinese sovereignty, and undermined peace, security, and order in the relevant sea areas", Hua said.

The rising military tension comes against the backdrop of an increasingly bitter trade war between China and the US.

The two countries have traded barbs over what United States said was Beijing's military installation building on artificial islands and reefs. China has built and militarized artificial islands in the sea in a bid to maintain its control.