Chinese dredging vessels are purportedly seen in the waters around Fiery Cross Reef in the disputed Spratly Islands in the South China Sea in this still image from video taken by a P-8A Poseidon surveillance aircraft provided by the United States Navy May 21, 2015. U.S. Navy/Handout via Reuters/File Photo

HANOI (Reuters) - U.S. President Barack Obama said on Tuesday that Washington would stand with partners to ensure freedom of navigation and flight in the South China Sea and, without mentioning China by name, said big nations should not bully smaller ones.

He was speaking on the second day of a visit to Vietnam, where on Monday he announced the complete lifting of the United State’s ban on sales of lethal weapons to the Southeast Asian country.