The Obama administration believes North Korea has most likely completed launch preparations and could test fire mobile ballistic missiles at any time based on the most recent intelligence, a U.S. official said.
A test launch of one or both of missiles thought to be loaded into mobile launchers could happen without North Korea issuing a standard warning to commercial aviation and maritime shipping, according to the official.
The official declined to be named because of the sensitivity of the information.
He cautioned most of the information comes from satellite imagery, so it's impossible to reach a definitive conclusion because the United States has no means to gather information on the ground.
"We hope they issue a notification but at this point we don't expect it. We are working on the assumption they won't, " the official said.
He said the launch could be "imminent" but also cautioned the United States "simply doesn't know."
The official, along with another Pentagon official, confirmed the United States has been able to keep satellites over the suspected launch area for most of the past week.
The United States believes the missiles remain at a point about half way down the eastern coast of North Korea and about 10 miles inland.
Imagery has been impeded by some bad weather which also means there is less than perfect knowledge about what is happening on the ground.
But based on what the United States has seen, the belief is that the missiles have received their liquid fuel and are ready for launch.
After any launch, U.S. satellites and radars in the region will be able to calculate within minutes missile trajectory and quickly conclude whether they are on a test path headed for open ocean or potentially headed for land areas, such as Japan, which could then force the United States and Japan to decide whether to try to shoot them down, both officials told CNN.