It is just the latest challenge from Washington to Beijing over the fate of the Spratly Islands, after the guided missile destroyer the USS Lassen last month sailed past a series of islets in Subi Reef in the Spratly chain.
It also comes ahead of a visit to Asia next week by President Barack Obama that will see territorial disputes at the fore of discussions with regional leaders, several of whom have claims in the resource-rich South China Sea.
"Both aircraft continued their mission without incident, and at all times operated fully in accordance with international law."
Washington has said that China's transformation of geographical features in the Spratlys into artificial islands capable of supporting military facilities poses a threat to freedom of navigation in the critical area.
Speaking to reporters today, Chinese foreign ministry spokesman Hong Lei said Beijing opposes "the action of undermining China's sovereignty and security under the pretext of freedom of navigation and overflight.