The United States again flew a surveillance aircraft over the Korean Peninsula, an aviation tracker said Tuesday, the latest in a series of flights to monitor North Korea amid growing concern Pyongyang may be gearing up for a long-range rocket launch.

The E-8C aircraft, or JSTARS, was spotted over the Korean Peninsula at 33,000 feet, Aircraft Spots said on its Twitter account without specifying the exact time of the operation. It also did not upload photos showing the flight route.

As a platform for airborne command and control, surveillance and reconnaissance, the E-8C is known to be capable of closely monitoring North Korea's troops and equipment movements, including missiles and artillery guns.

The flight, which followed the surveillance operation by the US RC-135W Rivet Joint, came amid heightened tensions on the peninsula after North Korea claimed to have conducted a "very important test" at its Sohae Satellite Launching Ground, better known as the Dongchang-ri site, on Saturday.

Though Pyongyang did not elaborate on details, military sources and experts believe that it tested a new high-thrust engine using liquid fuel with a goal to launch bigger, more powerful rockets for satellites or intercontinental ballistic missiles.

Stressing that the year-end deadline that Pyongyang set for Washington to come up with new proposals in nuclear negotiations is drawing near, North Korea recently warned that it is up to the US to choose what "Christmas gift" it will get.

The warning apparently means that if the deadline is missed, the North could restart testing of nuclear weapons and ICBMs in what would be a significant blow to US President Donald Trump ahead of next year's presidential election.

In recent weeks, the US has deployed several types of surveillance planes over the Korean Peninsula, including its Navy's P-3C maritime surveillance plane, the RC-135U Combat Sent, the RC-135W Rivet Joint and the RC-135S Cobra Ball aircraft. (Yonhap)