Chuck Hagel, the nominee to be U.S. secretary of defense, on Thursday emphasized the importance of bolstering alliances with South Korea, Japan and Australia to deal with North Korea, which he described as "quite unpredictable."

He said North Korea poses an actual threat to the U.S. and its regional allies, expressing his far-reaching views on pending national security issues at his Senate confirmation hearing.

"North Korea is beyond a threat," he said. "It's a real nuclear power and quite unpredictable."

Pyongyang, emboldened by a successful long-range rocket launch in December, is seen as preparing for another nuclear test.

Hagel, a Vietnam War veteran, pointed out the U.S. is rebalancing diplomatic efforts and military presence towards the Asia-Pacific region.

"We are in the process of modernizing our defense posture across the entire region to defend and deepen our partnerships with traditional allies, especially Japan, South Korea and Australia, to continue to defend against provocation from states like North Korea as well as nonstate actors," he said.

In written answers to advance policy questions before the hearing, Hagel said further sanctions are necessary to curb the communist nation's weapons development.

"The United States should continue to work to prevent North Korea's proliferation of weapons-related technology by advancing international nonproliferation norms and further tightening sanctions aimed at impeding development of North Korea's ballistic missile and nuclear programs," he said.

Meanwhile, the former Republican senator faced fierce attacks from his former colleagues throughout the hearing, heralding a tough confirmation process.

Sen. John McCain (R-AZ) grilled Hagel for his opposition to the troop surge in Iraq in 2007.

Also at issue is Hagel's mixed voting record on sanctioning Iran and past criticism of efforts to isolate both Syria and Hamas.

Hagel said history will judge his record. (Yonhap News)