The USS Lassen sailed close to a Chinese manmade island on Tuesday. Tensions have been mounting over China's territorial claims in the area.
China has criticized the sail-past of a US warship close to an uninhabited reef in the South China Sea that China has occupied. The US and others contest China's territorial claims there.
China has constructed islands in an area claimed by some of its neighbors. It says it has an exclusion zone around these islands, which is at odds with the US position.
Journalists, lawyers, and religious minorities have all raised concerns over China's crackdown on civil society. President Xi is making his first state visit to Washington this month.
Beijing put on an imposing display of its growing military clout and national pride as it celebrated the 70th anniversary of the end of World War II and the defeat of Japanese imperial forces.
Twenty-three people have now been detained in a broadening investigation of the port city's storage facility blasts, which killed more than 140.
Japan is worried that China is building 16 oil rigs in order to exploit oil reserves in the Japanese part of the sea.
A briefing on what China wants: It speaks of a 'peaceful rise' in Asia and of binding the region with liberal markets. But it's creating military bases and throwing sharp elbows far below its own territory.