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)