The US has sent a navy warship near an artificial island built by China in the disputed South China Sea as part of the first "freedom of navigation" operation under President Donald Trump, prompting Beijing to strongly condemn the "provocative action."
The guided-missile destroyer, USS Dewey, conducted a patrol within 20 kilometres of Mischeef Reef, part of the Spratly Islands.
A crucial shipping route, China claims ownership of the vast majority of the South China Sea, including the Paracel and Spratly island chains, a claim disputed by numerous other countries including the Philippines and Vietnam.
The Chinese government has reclaimed land and built up artificial islands in the sea, including on Mischief Reef, and deployed military assets to them.
The exercise is the first since October and comes after high-level visits and friendly exchanges between the US and China to settle trade issues and vows to cooperate to contain the nuclear programme of North Korea, a Chinese ally.
Pentagon spokesman Jeff Davis said, "We operate in the Asia-Pacific region on a daily basis, including in the South China Sea. We operate in accordance with international law."
The patrols are "not about any one country, or any one body of water," he told the Wall Street Journal.
In Beijing, China reacted sharply to the action saying the US warship had entered the South China Sea "without permission".
China's defence ministry said two Chinese frigates had "warned and dispelled" the US Navy ship after it had entered its waters "without permission."
"We firmly oppose the US behaviour of showing force and boosting regional militarisation, and have made solemn representation to the US side," defence ministry spokesman Ren Guoqiang said.
China's foreign ministry too criticised the US move.
"The act damaged China's sovereignty and security interests, and could have easily led to an air or sea accident," foreign ministry spokesman Lu Kang told reporters.
"[China] resolutely opposes any country sailing or flying freely that could pose damage to China's sovereignty and security interests. At present, through the joint efforts of China and Asean countries, the South China Sea situation has cooled down. The acts of the United States have seriously disrupted the process of dialogue and consultation. We urge the US to correct this mistake," he said.
A Pentagon official said that since 1979, the freedom of navigation programme has demonstrated non-acquiescence to excessive maritime claims by coastal states all around the world. It includes consultations and representation by American diplomats and operational activities by the US military forces.
In February USS Carl Vinson Strike Group arrived in South China Sea but did not conduct Freedom of Navigation Operations (FONOPS) against Chinese maritime claims around its artificial-island bases in the Spratly and Paracel islands.
Early this month, Pentagon spokesman Davis told foreign journalist that the FONOPS is a "routine activity" carried out by the US around the world.
"We did it last year, freedom of navigation assertions against 22 different countries all over the world. Many of those countries are friends and allies," he said.
"Unfortunately, I think the public narrative has made it about China and the South China Sea. It's not that. It's about asserting international rights to navigate in waters that international law accepts, and these are rights and benefits that benefit all countries on Earth, to include China," Davis said.
"We will continue to do them," he said.
In an annual FNOPS report released by the Pentagon in February, the Department of Defence said that in 2016 it carried out freedom of navigation operations against 22 countries, including India. Other major countries were Brazil, Indonesia, Iran, Italy, Japan, Malaysia, Oman, Pakistan, the Philippines, South Korea, Thailand, and Vietnam.