Two U.S. Navy warships sailed through the South China Sea this week, a move likely to inflame tensions in a region caught between the U.S. and China’s competing influence.

The littoral combat ship Gabrielle Giffords on Wednesday came within 12 nautical miles of islands claimed by China, Cmdr. Reann Mommsen, spokeswoman for the U.S. Navy’s Seventh Fleet, told Reuters.

That was followed on Thursday by the destroyer Wayne E. Meyer, challenging restrictions on passage through the Paracel Islands – which are occupied by China, Mommsen said.

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At a meeting of defense ministers in Bangkok earlier this week, Chinese Defense Minister Wei Fenghe urged the U.S. to “stop flexing muscles in the South China Sea and to not provoke and escalate tensions in the South China Sea.”

On Wednesday, U.S. Defense Secretary Mark Esper accused China of using coercion and intimidation against smaller Asian nations to impose its will in the South China Sea. He urged Vietnam and others in the region to push back.

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"We will not accept attempts to assert unlawful maritime claims at the expense of law-abiding nations," Esper said in a speech to the Diplomatic Academy of Vietnam, a government university.

The Associated Press contributed to this report.