The U.S. has delivered another RQ-4 Global Hawk surveillance drones to the Korean Air Force, according to Ambassador Harry Harris. In a tweet Sunday, Harris boasted the delivery marks a "great day" for the Korea-U.S. alliance.

He tweeted an image of a Global Hawk parked in the hangar of an air base with the national flags of the two countries on a wall behind. "Republic of Korea Air Force" is emblazoned on the fuselage.

The Global Hawk is a high-altitude spy plane that effectively works like a surveillance satellite capable of relaying military movements in real time.

A Global Hawk surveillance drone is parked in the hangar of an air base in Korea on Sunday, in this photo tweeted by U.S. Ambassador Harry Harris.

"Congratulations to the U.S.-ROK Security Cooperation teams on delivering Global Hawk to [Korea] this week," Harris tweeted using the abbreviation for "Republic of Korea."

Korea took delivery of the first Global Hawk from the U.S. late last year, so the one Harris mentioned is presumed to be the second one.

The envoy's tweet stirred some mutterings among officials here since the announcement would usually be made by the Defense Ministry, which has kept recent deliveries of U.S. armaments low-key for fear of agitating North Korea.

The military also kept the delivery of F-35A stealth fighter jets from the U.S. since March last year relatively quiet.

[Read this article in Korean]