The United States said it�s concerned by reports of China�s interference with oil and gas activities in the disputed waters of the South China Sea, where Vietnam accuses Beijing of violating its sovereignty.

State Department spokeswoman Morgan Ortagus said in a statement that China�s �repeated provocative actions aimed at the offshore oil and gas development of other claimant states threaten regional energy security and undermine the free and open Indo-Pacific energy market.�

Vietnam on Friday demanded China remove a survey ship from Vanguard Bank, which it says lies within Vietnam�s 200-mile exclusive economic zone. China claims the South China Sea almost in its entirety and has rattled smaller neighbors by constructing seven man-made islands in the disputed waters and equipped them with military runways and outposts.

Chinese coast guard vessels also have been reported near a drilling rig in the same Vanguard Bank area where Vietnam has contracted Russia�s Rosneft to develop gas fields.

�Vietnam has made contact with China on multiple occasions via different channels, delivered diplomatic notes to oppose China�s violations, and staunchly demanded China to stop all unlawful activities and withdraw its ships from Vietnamese waters,� Vietnam�s Foreign Ministry spokeswoman Le Thi Thu Hang said in a statement Friday.

Chinese Foreign Ministry spokesman Geng Shuang earlier in the week urged Hanoi to respect China�s sovereign rights and jurisdiction, �and not to take any move that may complicate matters.�

In May 2014, Chinese and Vietnamese vessels engaged in a dangerous confrontation when China�s national oil company moved its oil platform into waters Vietnam considers its territory.

Ortagus calls on China to �cease its bullying behavior and refrain from engaging in this type of provocative and destabilizing activities.�

(AP)