SEOUL, South Korea — In the dead of night on Saturday, American B-1B long-range bombers, escorted by F-15 fighter jets, prowled along North Korea’s east coast, in one of the United States military’s most daring maneuvers on the peninsula in decades.

Two days later, North Korea’s foreign minister, Ri Yong-ho, declared that Pyongyang had the right to shoot down American bombers even if they were outside its airspace — another escalation in the war of words between the North and President Trump.

But when those planes were near its shores, North Korea did nothing. South Korean intelligence officials told lawmakers on Tuesday that the North’s air-defense radar may have failed to detect their presence. Or, they said, Pyongyang may have simply chosen to avoid a confrontation.

Either possibility would seem to contradict the image North Korea has sought to project: that of a nuclear power eager and able to take on the United States. Behind the North’s belligerent rhetoric, some analysts see a leadership anxious to avoid a war it can’t win, and careful to leave itself a rhetorical way out even as it makes threats.