In early May, China National Offshore Oil Co. sent a rig to waters contested by both China and Vietnam. The tensions escalated this week when demonstrators in Vietnam protested against Chinese businesses.
Beijing said at least 10 of its nationals are missing following the demonstrations.
State Department spokeswoman Marie Harf said during her regular press briefing Thursday both sides were called on to find a peaceful resolution to the crisis. While the U.S. government has no stance on the claims to the territory, she said China's actions in particular were concerning.
"China's unilateral introduction of an oil rig was provocative," she said.
Vietnam said several hundred demonstrators were arrested following this week's melees.
Chinese Foreign Ministry spokeswoman Hua Chunying told staff at the Chinese Embassy in Vietnam that Vietnamese authorities should take their security obligations seriously.
"The Vietnamese side bears unshirkable responsibility for the violence against companies and nationals of China and other countries," she said Thursday.