The United States is shifting warships into position to track and possibly defend against a planned North Korean rocket launch while urging Pyongyang to cancel its second such attempt this year, the head of the U.S. Pacific Command said on Thursday.

Admiral Samuel Locklear, who commands U.S. forces in the Asia-Pacific region, said warships were being moved to the best locations to track the rocket during its launch and flight, which North Korea has set for sometime between December 10 and 22.

The United States is watching preparations for the launch "very closely," he told a Pentagon news conference. He said U.S. warships were being moved to monitor the rocket, as they were when Pyongyang attempted a similar launch in April.

"It should seem logical that we'll move them around so we have the best situational awareness," he said. "To the degree that those ships are capable of participating in ballistic missile defense, then we will position them to be able to do that."

Pyongyang says the launch aims to put a satellite into space. The United States and many other countries view it as a test of a long-range, nuclear-capable ballistic missile that would violate U.N. resolutions and further destabilize the Korean Peninsula. The North Korean launch attempt in April failed.

Locklear said the repositioned U.S. ships would help answer a series of questions.

"If they do violate the Security Council and launch a missile, what kind is it? What is it about? Where does it go? Who does it threaten? Where do the parts of it ... that don't go where they want it to go, where do they go? And what are the consequences of that?" he said.

The admiral said his main concern was reassuring U.S. allies that the United States was effectively monitoring the situation.

"We believe it is still contradictory to the U.N. Security Council resolutions ... because of the nature of the type of missile that they will be firing and the implications it has for ballistic-type of activity somewhere down the road and the destabilizing impact that will have on the security environment throughout the region," Locklear said.

He said there had been signs that the government of new leader Kim Jong-un would take a more "rational approach" to how it deals with its economy, its citizens and its international relationships.

Kim took power after the death of his father, former leader Kim Jong-il, on December 17. The anniversary of his father's death falls during the time frame set by North Korea for the rocket launch. Presidential elections in neighboring South Korea take place two days later, on December 19.

Locklear said while there was hope for a shift in North Korea's political direction, Pyongyang was once again poised to violate U.N. Security Council resolutions regarding its nuclear program.

"We encourage the leadership in North Korea to consider what they are doing here and the implications on the overall security environment on the Korean Peninsula, as well as in Asia," he said.