The United States and Vietnam began joint naval exercises Monday off the coastal town of Da Nang as a territorial dispute with China simmers, DPA reported.
About 1,400 US personnel are taking part in the week-long event, the third of its kind since 2010, Lieutenant Commander Mike Morley said.
The drills come as the Philippines and the US enter the second week of war games in that South-East Asian country. China warned that the timing of the exercises could provoke armed confrontation amid the dispute over waters near the Scarborough Shoal.
Morley denied any significance in the timing of the exercises in Vietnam.
"The two are completely unrelated," he said. "The exercise in Vietnam was coordinated about one year ago.
"We have seen since the US and Vietnam normalized relations several years ago there is a steady progression every year in those relations growing stronger and the countries growing closer," he said.
Beijing complained about last year's drills in Vietnam. They came shortly after Vietnam and the Philippines accused China of disrupting energy exploration in disputed areas of the South China Sea.
China lays claim to the entire sea, which straddles key shipping lanes in the region and is believed to be rich in resources. Malaysia and Brunei also have overlapping claims to the area.
The US has said it has a national interest in promoting freedom of navigation in the sea.