BEIJING — Two Chinese fighter jets flew too fast and too close to an American military aircraft patrolling the East China Sea, prompting a formal protest to the Chinese government, the United States Air Force said on Friday.

The episode on Wednesday involved an American WC-135 Constant Phoenix aircraft and two Chinese SU-30 jets that both flew in an “unprofessional” and dangerously close way, according to a spokeswoman for the Pacific Air Forces, Lt. Col. Lori Hodge.

The United States has complained to China through diplomatic and military channels, she said in a statement. The “speeds and proximity” of the two Chinese planes, coupled with the “maneuvers” of one of the pilots, raised the concerns, she said.

The WC-135, a modified Boeing C-135, is designed to detect radioactive debris after the detonation of a nuclear device and is informally known as a “sniffer.” The Chinese Ministry of National Defense did not reply to request for comment.