The Pentagon deployed RC-135W, E-8C, RQ-4 Global Hawk and RC-135S aircraft capable of geolocating signals and capturing aerial images and with other reconnaissance and surveillance functions said Aircraft Spots, a Twitter account dedicated to monitoring military air movements, reported Efe news.
Although the US Air Force had flown some of these planes separately in recent weeks, the unusual occurrence of flying all four of them at the same time showed growing attention the US is giving to Pyongyang's return to belligerence, according to experts.
The regime led by Kim Jong-un has conducted several short-range missile tests in recent months and has implied that it could resume its nuclear tests and with intercontinental ballistic missiles (ICBM), to which Washington has responded with an important deployment of military surveillance.
The US air operation also responded to Pyongyang's warning to send a "Christmas gift" to Washington if the latter does not come up with a new proposal in the denuclearisation dialogue.
When asked about the North Korean threat at his Mar-a-Lago resort in Florida on Tuesday, US President Donald Trump said that he would deal with any "Christmas gift" "very successfully."
"Maybe it's a nice present. Maybe it's a present where he sends me a beautiful vase as opposed to a missile test," he added before sending a Christmas greeting to the members of several army units deployed in various locations around the world.
North Korea held an important plenary session over the weekend in which "important organisational and political measures and military steps" were discussed, and has given the US time until the end of the year to raise a new offer.
Bilateral negotiations have not advanced since the failed February summit in Hanoi, where Washington considered Pyongyang's offer regarding the dismantling of its nuclear assets insufficient and refused to lift economic sanctions.
Since then, Kim's regime has repeatedly conducted weapons tests and hardened its rhetoric towards the White House.
( With inputs from IANS )