Tensions have escalated between the US and China after the former sent a navy warship near an artificial island in the disputed South China Sea as part of the first "freedom of navigation" operation under President Donald Trump.
The move by the US has prompted China 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. 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 anybody of water," he told the Wall Street Journal in a statement.
The "freedom of navigation" operation is a signal intended by the US to assert its intention to keep critical sea lanes open, The Hill newspaper reported.
"In conducting the freedom of navigation patrol, President Trump is likely to anger China at a time when the USis seeking increased cooperation with the country to help rein in North Korea," it said. China claims almost all of the South China Sea. ButTaiwan, the Philippines, Brunei, Malaysia, and Vietnam have rival claims over the region.
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 US diplomats and operational activities by US military forces, another Pentagon official said.
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, Davis told foreign journalist that the FONOPS is a routine activity carried out by the US around the world.
"We did last fiscal year, freedom of navigation assertions against 22 different countries all over the world.Many of those countries are friends and allies," he said.
"It's not about one country. It's not about one body of water. 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 do these. We will continue to do them," the Pentagon spokesman 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.