On Wednesday, the two Chinese SU-30 jets approached a WC-135 Constant Phoenix aircraft conducting a routine mission in international airspace in accordance with international law, Pacific Air Forces spokeswoman Lt. Col. Lori Hodge said in a statement.
US to talk privately with China
The WC-135 crew characterized the intercept as unprofessional "due to the maneuvers by the Chinese pilot, as well as the speeds and proximity of both aircraft," Hodge said.
She declined to provide further details and said the issue would be addressed with China through "appropriate diplomatic and military channels."
China declared an air defense identification zone over a large section of the East China Sea in 2013, a move the U.S. called illegitimate and has refused to recognize.
China has demanded foreign aircraft operating within the zone declare their intentions and follow Chinese instructions. Hodge declined to say whether Wednesday's incident was within the self-declared Chinese zone.
"U.S. military aircraft routinely transit international airspace throughout the Pacific, including the East China Sea," she said. "This flight was no exception."
Japan and China
Japan scrambled fighter jets Thursday after four Chinese coast guard vessels entered what Japan considers its territorial waters near disputed East China Sea islets and a dronelike object flew near one ship, Japan said.
It was the first such flight near the islands witnessed by Japanese officials, although the incident took to 13 the number of intrusions this year by Chinese coastguard ships in the contested waters, Japan's coastguard said.
Japan and China have long been at loggerheads over the tiny, uninhabited islands, called the Senkaku in Japan and Diaoyu in China. They are controlled by Japan but claimed also by China.
Defense Minister Tomomi Inada said two F-15 fighter jets, one E-2C early warning aircraft and an AWACS surveillance plane were sent to the scene.
In Beijing, Chinese Foreign Ministry spokeswoman Hua Chunying said the drone had been released by 'relevant media' for aerial photography, rather than by the coast guard, but did not name the organization.
Reuters contributed to this report.