A US Air Force WC-135R Constant Phoenix, commonly known as a "nuclear sniffer," was spotted near the Taiwan Strait, southwest of Taiwan, on Sunday. The military aircraft collects airborne particles and gases to detect radioactive material. Its appearance on flight-tracking data comes amid China's unannounced war drills simulating a blockade and attacks on Taiwan.

The Flightradar24 playback shows the USAF sniffer jet on a round-trip flight from Okinawa, traveling south of Taiwan and into waters southwest of the island, near the southern approaches to the Taiwan Strait.

The aircraft's specific mission and any connection to China's military drills remain unconfirmed.

The USAF uses the aircraft to detect radioactive particles and gases, helping US intelligence analysts identify and assess nuclear activity in a given area. 

Notably, the aircraft does not directly locate nuclear warheads or see inside underground facilities. Its flight near southern Taiwan does not establish that radiation was detected or that a nuclear event occurred.

The aircraft also conducts routine sampling missions worldwide, but this flight comes as China's military drills around Taiwan have heightened fears of a blockade that could snarl maritime traffic in the region. 

Here's what we've reported:

Also worth noting: President Donald Trump is scheduled to arrive in Shenzhen, China, late Wednesday to attend the APEC summit.