North Korea threatened Wednesday to shoot down any US spy planes that intrude into its airspace ahead of a planned rocket launch. North Korea said it will send a communications satellite into orbit on a multistage rocket between April 4 and 8. The US, South Korea and Japan think the reclusive country is using the launch to test long-range missile technology, and they warn Pyongyang would face sanctions under a UN Security Council resolution banning the country from ballistic activity. Pyongyang's state radio accused US RC-135 surveillance aircraft of spying on the launch site on its northeast coast, according to South Korea's Unification Ministry, which is in charge of monitoring the North. "If the brigandish US imperialists dare to infiltrate spy planes into our airspace to interfere with our peaceful satellite launch preparations, our revolutionary armed forces will mercilessly shoot them down," the ministry quoted the radio as saying. It was unclear what capability the North Korea has to shoot down the high-flying Boeing RC-135, which can reach altitudes of nearly 15 kilometers high. The threat came a day after the North claimed the US and South Korea conducted about 190 spy flights over its territory in March, including over the sea off the launch site.