The United States on Thursday urged North Korea anew not to launch a long-range rocket after a pro-Pyongyang newspaper hinted of a new nuclear test in the expected fallout from its plans.

Choson Sinbo, a newspaper in Japan that generally reflects North Korea's official thinking, warned that Pyongyang's moratorium on nuclear tests "can be canceled" if the United States ends plans for food aid.

"My response is -- what we've said very clearly is that we don't want to see the satellite launch. I'm not going to speculate down the road," State Department spokesman Mark Toner said of the threat.

"We believe that this satellite launch would be in violation of the existing UN Security Council resolutions," he said.

North Korea says it will launch a satellite between April 12 and 16 amid celebrations for the 100th birth anniversary of its founder Kim Il-Sung but the United States and other countries see it as a pretext for a long-range missile test.

"We are monitoring very closely the prospect of a missile launch. We take this prospect very seriously," said Pentagon spokesman George Little.

"We have the means at our disposal to track very closely what's happening," he added.

Pyongyang in February agreed to suspend operations at its Yongbyon uranium enrichment plant and impose a moratorium on long-range missile tests and nuclear tests, in return for 240,000 tonnes of US food aid.

Washington last week said it was suspending plans to start food deliveries in light of the imminent rocket launch.

North Korea has said it would welcome foreign observers to the launch. Toner said the United States has not received any invitation, which Pyongyang would ordinarily send to the NASA space agency.