The U.S. government has "noted" North Korea's multistage rocket launch and it is preparing for a formal response, an official said Tuesday.

"We have noted the launch and we are monitoring the situation," a U.S. administration official told Yonhap News Agency, requesting anonymity. "We will have further official comment at a later time."

A Pentagon official also said the U.S. military plans to issue a statement on the trajectory of the North Korean rocket.

The first informal responses came about two hours after the North's rocket launch reportedly at 7:51 p.m. local time.

Pyongyang has claimed the launch was successful.

The U.S. government's cautious attitude toward the rocket launch marks a contrast to its swift response to Pyongyang's April launch, which ended in failure.

Earlier, an official at the White House hurriedly hung up the phone, only saying she can't talk to media about the North's move "for now."

Officials at the North American Aerospace Defense Command

(NORAD) and U.S. Northern Command (USNORTHCOM) were not available for comments.

In April, NORAD and USNORTHCOM distributed a statement describing North Korea's multistage rocket launch as a failure.

The White House was quick to denounce the launch as "provocative" despite the failure. (Yonhap News)