North Korea is preparing to launch a short- or medium-range missile, possibly right after it carries out its plan to fire a long-range rocket in early April, a Japanese newspaper reported Sunday.

North Korea says it will launch a communications satellite into orbit between April 4 and 8 as part of its space development program. Regional powers, however, suspect the North is using the launch to test long-range missile technology, and have warned it could face international sanctions under a 2006 U.N. Security Council resolution prohibiting ballistic activity by North Korea.

U.S. officials said last week that North Korea has mounted a rocket onto its northeast coastal Musudan-ni launch pad, putting the country well on track for a launch. U.S., South Korean and Japanese officials have warned they will take the North to the U.N. Security Council if it goes ahead with its plan.

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Tokyo's Sankei newspaper, citing several unnamed Japanese government sources, reported Sunday that the North is also preparing to test-launch another missile from Wonsan, about 155 miles south of Musudan-ni. It said U.S., South Korean and Japanese intelligence analyses said the missile could be short or medium range.

The report said the North may conduct another missile test if the U.N. Security Council approves sanctions against it, or if it cannot wrest concessions from the United States.

Japan's Defense Ministry declined to comment on the Sankei report. South Korea's Defense Ministry and National Intelligence Service — its main spy agency — said they couldn't immediately confirm the report.

North Korea warned last week it would take "strong steps" if the Security Council even criticizes the launch, suggesting it will reverse the steps it has taken so far to disable its nuclear facilities if sanctions are levied.

Under a 2007 deal with the U.S., South Korea, China, Russia and Japan, North Korea agreed to dismantle its nuclear program in exchange for aid. The process has been stalled, however, by a dispute over how to verify the North's accounting of its past nuclear activities.

South Korea's foreign minister said in an interview published Sunday that the U.N. ambassadors of South Korea, the U.S., China, Russia and Japan have begun discussing how to respond to North Korea's rocket launch.

"We can't let it pass as if nothing happened if (the North) violates the Security Council resolution," Yu Myung-hwan was quoted as saying by the mass-circulation JoongAng Ilbo newspaper. "An appropriate U.N. measure based on the five countries' common stance will come out."

Sankei said in a separate dispatch from Washington that 15 personnel from the Iranian satellite and missile development company Shahid Hemmat Industrial Group are staying in North Korea at the invitation of the North Korean government.

Quoting unnamed intelligence sources in Washington it said are close to North Korean affairs, Sankei said the Iranians are likely to join North Korean preparations for the launch and also observe it. The report said North Korea sent missile experts to Iran when it launched a satellite in February.

North Korea is believed to have sold missiles to Iran, and Iran's Safir-Omid space launch vehicle owes much to the North's Taepodong missile.

Japanese and South Korean officials were not immediately available for comment on the report.

Experts in Seoul say the North is likely to go ahead with the rocket launch after having announced it, but the exact timing depends on weather conditions and technical issues.

"It's unthinkable" for North Korea to cancel its plan now, said Paik Hak-soon, an analyst at the private Sejong Institute think tank outside Seoul.

Paik said North Korea would not want to be seen as bowing to international pressure and would not want lose what it views as a good opportunity to bolster its leverage with President Barack Obama's administration as it formulates its policy toward the North.