US aircraft carrier USS Nimitz left the South China Sea on Monday morning heading west, according to data from ship tracking website Marine Traffic, Reuters reports.

The carrier had planned to visit Danang City, Vietnam later this week, but two sources, including one diplomat, said a formal reception slated for Friday had been called off.

One of the sources said the US Embassy in Hanoi had informed him about the cancellation, due to "an emergent operational requirement.”

The embassy didn't immediately respond to a Reuters request for comment.

The Nimitz Carrier Strike Group conducted maritime security operations in the South China Sea last week, as "part of the U.S. Navy's routine presence in the Indo-Pacific," according to the website of the Commander of the U.S. Pacific Fleet."