The United States has moved naval ships with ballistic missile defense to the periphery of the Korean Peninsula to keep close tabs on Pyongyang's possible rocket launch, the top U.S. military commander in Asia and the Pacific said Thursday.

"It should seem logical that we will move them around so we have the best situational awareness," Adm. Samuel Locklear, head of the U.S. Pacific Command, said at a press conference in the Pentagon.

He commands the 325,000-strong forces that have become more vital in the U.S. defense strategy, which is rebalancing its diplomacy and military presence toward Asia.

He said North Korea is apparently trying to hone its missile technology after nuclear tests in 2006 and 2009.

"They have progressively gained better technology over time, and they have progressively gained that through a number of methods over a number of years and decades," he said.

But he would not predict whether the North's long-range rocket launch, scheduled between Dec. 10 and 22, will be successful, unlike the previous launch in April.

"We do watch this very carefully, watch it very closely," he said.

U.S. media reported earlier that two U.S. guided-missile destroyers -- the USS Benfold and the USS Fitzgerald -- have been sent to the area to monitor the situation.

On North Korea's leadership, the admiral said, "We are still in the wait-and-see stages."

He pointed out some signs of possible change.

"There have been, I think, a number of signs that might lead you to believe that the new regime leadership is going to take a more, I would say, rational approach to how they deal with their own economy and how they deal with their own people and how they deal internationally," he said.

Locklear urged Pyongyang to rethink its rocket plan in consideration of "the implications on the overall security environment" in the region. (Yonhap News)