The United States flew another surveillance aircraft over the Korean Peninsula, an aviation tracker said Monday, the latest in a series of flights to monitor North Korea amid growing concerns Pyongyang could launch long-range missiles.

The US Air Force RC-135W Rivet Joint was spotted flying over the peninsula at 31,000 feet, Aircraft Spots said without specifying the exact time of the operation.

The same type of surveillance aircraft made a flight over the peninsula over the weekend, the aviation tracker tweeted on Sunday, noting that it is "actually odd timing" as it does not carry out operations "usually ... on weekends." 

A few days ago, US Navy's EP-3E plane also conducted similar surveillance operations.

The series of flights took place when North Korea has threatened to take a "new way" other than dialogue, if the US fails to meet its year-end deadline to make concessions in their stalled denuclearization negotiations.

Warning that the deadline is drawing near, the North said it is entirely up to the US to decide what "Christmas gift" it would get, deepening concern that the regime could conduct an intercontinental ballistic missile launch.

Earlier this month, the North conducted what appeared to be two rocket engine tests at its western satellite launch site in what could be a prelude to the launch of a long-range satellite-carrying rocket or an ICBM.

As the North has taken a series of military moves, such as successive firings of short-range ballistic missiles and a submarine-launched ballistic missile, the U.S. has deployed several types of surveillance planes over the peninsula more often than before. Sources and experts see those operations, at least in part, as designed to send warning messages against the bellicose regime. (Yonhap)