North Korean leader Kim Jong Un appears more "risk-tolerant, arrogant and impulsive" than his father as he forges ahead with military programs that have left even China — Pyongyang's top ally — feeling frustrated, a top U.S. general said on Tuesday.

Army Gen. Vincent Brooks, who is President Barack Obama's nominee to lead American forces in South Korea, told a Senate hearing that he was "not optimistic" about North Korea's direction.

The reclusive state conducted a fourth nuclear test in January and a long-range rocket launch in February, both in contravention of U.N. Security Council resolutions. Last week, it failed to launch what the United States believes was an intermediate-range ballistic missile.