Missile and launch components have been moved to the east coast of North Korea in the "last few days," a U.S. official with direct knowledge of the information told CNN Thursday.
The apparent deployment comes amid further threatening statements by North Korea and heightened tensions in the region -- a situation that "does not need to get hotter," a U.S. State Department spokeswoman said.
The move of the missile and launch equipment could mean that Pyongyang, which unleashed another round of scathing rhetoric accusing the United States of pushing the region to the "brink of war," may be planning a missile launch soon.
The components, the official said, are consistent with those of a Musudan missile, which has a 2,500-mile range, meaning it could threaten South Korea, Japan and Southeast Asia.
The United States has been looking for a hidden North Korean east coast launch site or mobile launchers, a concern because a launch from the east coast would go over Japan, the official said.
It is believed a missile launch would be a "test" launch rather than a targeted strike. That is because it appears the North Koreans have only moved the components so far. The United States is waiting to see whether North Korea issues a notice to its airmen and mariners to stay out of the region.
Communication intercepts in recent days also seem to show that Pyongyang might be planning to launch a mobile ballistic missile in the coming days or weeks, another U.S. official said.
Earlier, South Korean Defense Minister Kim Kwan-jin told a parliamentary committee in Seoul that the North has moved a medium-range missile to its east coast for an imminent test firing or military drill.
The missile doesn't appear to be aimed at the U.S. mainland, Kim said, according to the semi-official South Korean news agency Yonhap.
Wednesday, the United States announced it was sending ballistic missile defenses to Guam, a Western Pacific territory that is home to U.S. naval and air bases. North Korea has cited those bases when listing possible targets for missile attacks.
The latest developments come amid the disclosure of what one U.S. official calls an Obama administration "playbook" of pre-scripted actions and responses to the last several weeks of North Korean rhetoric and provocations.
Pentagon seeks to 'turn the volume down'
Pentagon officials, while decrying North Korean saber-rattling, said recent announcements of U.S. military deployments in response to belligerent statements by North Korea may have contributed to the escalating tensions between the countries.
As the bombast reaches a fever pitch, the United States is refining its message toward North Korea. The Pentagon now says it is working to decrease the temperature as it maintains a frank and vigilant stance toward Pyongyang's threats.
"We are trying to turn the volume down," a Defense Department official said.
"We accused the North Koreans of amping things up, now we are worried we did the same thing," one Defense Department official said.
State Department spokeswoman Victoria Nuland denied that there had been a change in tone and defended the U.S. responses.
"The moves that we have been making are designed to ensure and to reassure the American people and our allies that we can defend the United States, that we will and that we can defend our allies," she said.
It was the ratcheting of tensions from North Korea that led to the U.S. shoring up its defense posture, she said.
"But we have also been saying all the way through that this does not need to get hotter, that we can change course here" if North Korea cooperates with the international community.
At the same time, National Security Council spokeswoman Caitlin Hayden said, the United States urged North Korea's leaders "to heed President Obama's call to choose the path of peace and come into compliance with its international obligations."
"Threats and provocative actions will not bring North Korea the security, international respect, and economic development it seeks," she said.
North Korea slams U.S.
The latest tough talk from Pyongyang lashed out at the U.S. military presence in the region.
A spokesman for a North Korean group accused the United States of "hurling" its "nuclear war hardware into the region and pushing the situation on the brink of war," Pyongyang's official news agency reported.