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The US has sent a navy warship near an artificial island in the disputed South China Sea. The warship is sent as part of the first "freedom of navigation" operation under President Donald Trump prompting the Chinese government to say that the "provocative action" violated its sovereignty.
The guided-missile destroyer, USS Dewey, conducted a patrol within 20 kilometres of Mischeef Reef, part of the Spratly Islands over which several countries, including China, have competing claims.
The exercise is the first since October and comes after 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.
But China reacted promptly to the action saying the US warship had entered the South China Sea "without permission".
"The relevant action taken by the US vessel undermines China's sovereignty and security interests," foreign ministry spokesman Lu Kang told reporters.
"We urge the US to correct this mistake," he said.
"Stop taking further provocative actions that hurt China's sovereignty and maritime interests, so as to avoid hurting peace and security of the region and long-term cooperation between the two countries."
In another report, to American news website The Hill reported that the "freedom of navigation" operation was a signal intended by the US to assert its intention to keep critical sea lanes open.
"In conducting the freedom of navigation patrol, President Trump is likely to anger China at a time when the US is seeking increased cooperation with the country to help rein in North Korea," it said.
China claims almost all of the South China Sea. But Taiwan, the Philippines, Brunei, Malaysia, and Vietnam have rival claims over the region.
A Pentagon official said, however, 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, Philippines, South Korea, Thailand, and Vietnam.