North Korea’s air force has sharply increased jet fighter training flights in the past few days, with the number of sorties reaching as many as 700 on the day South Korea and the United States launched a joint war game earlier this week, a military source in Seoul said Wednesday.

The North’s move is seen as part of efforts to beef up combat readiness and to closely monitor joint drills in the South that began on Monday. The drill, called Key Resolve, involves about 10,000 Korean troops and 3,000 American personnel as well as military weapons and equipment, including F-22 stealth jets and B-52 bombers deployed from overseas U.S. bases.

“Flights of the North Korean air force’s fighter jets and helicopters reached about 700 sorties on March 11,” the source said on the condition of anonymity. “It is seen as unprecedented in scale.”

The recent sortie is nearly six times more than the maximum number of flights in a day during last year’s summer training, the source said.

The impoverished nation is known to have restricted flying time to save hard currency as its fighter jets depend on imported fuel.

North Korea is believed to have accumulated about 1.5 tons of fuel for wartime use, according to military officials.

The latest move comes as the communist nation is preparing a mass military drill along its eastern coast, and activities of submarines and warships have also increased along its east and west coasts.

Recent satellite imagery shows no sign North Korea is readying another long-range rocket launch within the next month or another nuclear test, a U.S. research institute said Tuesday.

North Korea has previously announced it would conduct more rocket launches and has also hinted at a follow-up to its Feb. 12 atomic test.

Very little is going on at the Sohae site on the west coast from where a satellite was launched in December, according to an analysis written for 38 North, the website of the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies. There has been recent activity at the older Tonghae launch site on its northeast coast, although it’s unclear to what end.

Joel Wit, the 38 North editor and a former State Department official, said that as of end February, aerial photos also showed no indications of another nuclear test ― although preparations for such an underground blast are more tricky to detect.

“While inter-Korean rhetoric is heating up,” Wit said, “Pyongyang is unlikely to do anything provocative in the near-term” at least in terms of testing its weapons of mass destruction.

James R. Clapper, the director of the U.S. National Intelligence warned Tuesday an erratic North Korea, with its nuclear weapons and increasingly belligerent tone, poses a serious threat to the United States and East Asia nations, in the annual accounting of the threats worldwide.

“These programs demonstrate North Korea’s commitment to develop long-range missile technology that could pose a direct threat to the United States, and its efforts to produce and market ballistic missiles raise broader regional and global security concerns,” Clapper told the Senate Intelligence committee.

While the intelligence community has figured that Pyongyang’s nuclear efforts are designed for deterrence, worldwide prestige and coercive diplomacy, Clapper conceded that the United States does not know what would be the trigger that would prompt North Korea to act to preserve Kim’s regime.

Pressed during the hearing, Clapper said he was “very concerned” about Kim’s actions, which have included tough talk as well as a recent invitation to former basketball star Dennis Rodman.

“The rhetoric, while it is propaganda-laced, is also an indicator of their attitude and perhaps their intent,” Clapper said. “So for my part, I am very concerned about what they might do. And they are certainly, if they chose ... could initiate a provocative action against the South.”

Testifying before the Senate Armed Services Committee, the general in charge of U.S. Strategic Command said he is “satisfied” that existing U.S. missile defenses can defend against a limited attack from North Korea.

Air Force Gen. Robert Kehler also said he is confident the country is adequately defended from a limited attack by Iran, “although we are not in the most optimum posture to do that today.”

The Intelligence panel hearing also sought, in part, to rebuild some trust between the nation’s top intelligence officials and senators who complain they have been refused administration documents and other information that are necessary for congressional oversight.

(From news reports)