US concerned over China's 'interference' in South China Sea

The U.S. says 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 says Beijing violated its sovereignty.

State Department spokeswoman Morgan Ortagus says 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.

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