North Korea did not take any immediate action in response to US strategic bombers' flight near its east coast last week, Seoul's spy agency said Tuesday, noting it might have failed to fully detect the warplanes.

During its parliamentary briefing, the National Intelligence Service also said that after Washington's show-of-force measure Saturday, Pyongyang was seen readjusting the position of its warplanes and strengthening its coastal defenses, according to Lee Cheol-woo, the chief of the National Assembly's intelligence committee.

Escorted by F-15 fighters from Kadena Air Base in Okinawa, US B-1B Lancer bombers from Andersen Air Force Base in Guam carried out a rare nighttime flight mission in international airspace north of the Northern Limit Line, a de facto inter-Korean sea border. Washington said the flight underscores the seriousness with which it takes the North's "reckless behavior."
 

"We (lawmakers) heard (from the NIS) that as the flight was close to midnight, the North might have not anticipated it at all, or the North might have been unable to take action as its radar or other systems could not clearly detect it," Lee told reporters.

The absence of any military response from the pugnacious state has sparked speculation that it was unable to keep its radar system fully operational due to an electricity shortage. Some argue it intentionally avoided any action as the flight was carried out in international airspace.

The North is known to have an early warning radar system that has a detection range of up to 600 kilometers.

During its briefing, the spy agency also confirmed that the B-1B mission followed consultations between Seoul and Washington.

Seoul has sought to quell claims that the US-only flight suggests Washington could stage a military operation without consulting it first.

The Assembly's intelligence committee chief also said, citing the NIS's report, that the North is being cautious not to cause any accidental military clash along the tense land border, and that it has directed its armed forces to "report first before taking any military measures." (Yonhap)