Quoting U.S. intelligence analysts and officials, CNN and Fox News said U.S. spy satellites have detected activities which could be preparations for nuclear explosion tests at three North Korean sites.

CNN also said that latest U.S. intelligence show that North Korea's missile sites remain at a "very high state of readiness," and Pyongyang could use them "in the next several days."

On Tuesday, NBC News reported that the North Korean military has told China that it intends to conduct a "series of underground nuclear tests."

According to ABC News, meanwhile, a North Korean diplomat said Wednesday it would be "natural" for North Korea to conduct a second nuclear test.

In an interview with the U.S. television, Ri Gun, director general of the North Korean Foreign Ministry's American affairs bureau, said, "Even if there's a nuclear test, that is natural."

Ri did not reveal the timing or the scale of the prospective nuclear test.

Asked if the United States should not be surprised by the second test, Ri reportedly said that was the case.

Ri added that there are "many nuclear weapons" in South Korea and Japan and that they are conducting new military exercises, the report said.

Ri also said North Korea declared last year it has nuclear weapons, and said Pyongyang proved through its nuclear test that it possesses nuclear weapons peacefully, according to the report.