State media has said the rocket will be carrying an experimental satellite but officials in South Korea, Japan and the US have said they believe the launch is cover for a test of a new long-range missile.
Both Japan and the US have deployed missile interceptors and say they will shoot down the rocket if it poses a threat.
North Korean radio on Wednesday denounced what it said were intensifying flights by US and South Korean spy planes monitoring the launch site.
|The anticipated launch has triggered
protests in South Korea [Reuters]
"Should the US imperialist racketeers dare to intrude espionage planes into our territorial sky, interfering with our preparations for a satellite launch for peaceful purposes, our revolutionary forces will shoot them down unsparingly," it said.
The official Korean Central News Agency said a day earlier that US and South Korean planes had conducted "intensive" espionage against strategic targets every day from March 9 to 20.
"This is a wanton infringement upon the sovereignty of the DPRK (North Korea) and another dangerous military provocation to it," KCNA said.
Commenting on the latest satellite photos, the Washington-based for Institute for Science and International Security said the images showed that North Korea was no longer trying to hide the rocket from view.
"Since the missile is so easily seen in this image versus in imagery over the past several days since March 24, it is likely that North Korea was previously shrouding the missile," analysts from the arms control group wrote on its website.
US intelligence and military officials have not made any comment on the satellite images.
Gordon Brown, the UK prime minister, on Tuesday joined international calls for North Korea not to go ahead with the rocket launch.
Speaking in London after a meeting with South Korea's president, Brown said a North Korean launch would be in breach of United Nations resolutions.
The US has said warned North Korea that any move to launch the rocket will result in further sanctions and international isolation.