SEOUL (AFP) - North Korea threatened Wednesday to shoot down any US spy planes if they violate its airspace to monitor an imminent rocket launch, in a statement carried by state radio.

The warning followed accusations Tuesday that US planes had stepped up flights over a northeastern region where the North is preparing to launch the rocket.

The North has said it would launch a communications satellite some time between April 4-8. The United States, South Korea and Japan say this is a cover for a long-range ballistic missile test.

On Wednesday the North's Korean Central Broadcasting Station denounced US spy planes for monitoring launch preparations.

"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 North has regularly published its count of spy flights by South Korea and the United States.

The official Korean Central News Agency said Tuesday that US and South Korean planes had conducted "intensive" espionage against strategic targets every day from March 9 to 20.

It said a US RC-135 plane made shuttle flights between its Musudan-ri missile base and the northeastern port of Wonsan on March 13, 17 and 22.

"This is a wanton infringement upon the sovereignty of the DPRK (North Korea) and another dangerous military provocation to it," KCNA said.

US spy planes are within the range of counterstrikes, it said.