"China’s repeated provocative actions aimed at the offshore oil and gas development of other claimant states threatens regional energy security and undermines the free and open Indo-Pacific energy market," the State Department said in a statement.

It said these acts were interfering in particular with "Vietnam’s long-standing exploration and production activities" in the waters.

China claims almost the entire South China Sea, including waters close to Taiwan and Southeast Asian countries Brunei, Indonesia, Malaysia, the Philippines, Vietnam.

The State Department cited Secretary of State Mike Pompeo’s comments earlier this year when he said, "by blocking development in the South China Sea through coercive means, China prevents ASEAN members from accessing more than $2.5 trillion in recoverable energy reserves."

The department said that China’s reclamation and militarization of disputed outposts in the waterway, including the use of maritime militia to intimidate, coerce, and threaten other nations, undermine the peace and security of the region.

"The United States firmly opposes coercion and intimidation by any claimant to assert its territorial or maritime claims," it said.

"China should cease its bullying behavior and refrain from engaging in this type of provocative and destabilizing activity," it said.

Vietnam on Friday demanded that China withdraw oil survey vessel Haiyang Dizhi 8and its escorts from Vietnamese waters, accusing the ships of violating the country's exclusive economic zones and continental shelf. Vietnam calls the waters the East Sea.

Le Thi Thu Hang, spokeswoman of Vietnam's Foreign Ministry, said Vietnam has contacted China on multiple occasions via different channels, delivered diplomatic notes to oppose China's violations and staunchly demanded that China stop all unlawful activities and respect Vietnam's sovereign rights and jurisdiction over its waters, which would serve the interests of bilateral relations as well as regional stability and peace.

Vietnamese authorities at sea have employed a range of of appropriate measures to exercise Vietnam’s sovereignty, sovereign rights and jurisdiction in a peaceful and lawful manner for safeguarding Vietnamese waters, she added.