North Korea has denied that its upcoming satellite launch will breach an agreement with the United States, and blasted South Korea for a "smear campaign" against the widely criticised plan.

The North says it will launch a long-range rocket between April 12 and 16 to put a satellite into orbit. The United States and other nations see it as a thinly veiled missile test which would breach a United Nations ban.

Washington says it would also violate a February bilateral deal, under which Pyongyang agreed to suspend long-range missile tests while receiving US food aid.

"The launch of the working satellite is an issue fundamentally different from that of a long-range missile," Pyongyang's official news agency KCNA said in a commentary late Monday.

There are more than 100 worldwide launches of space vehicles a year on average and North Korea's own exercise is purely for scientific purposes, KCNA said.

"The South Korean puppet forces are busy with an odd smear campaign over the issue," the agency said, accusing Seoul's conservative government of trying to derail the North's US agreement to preserve its own influence with Washington.

Pyongyang's most recent long-range launch on April 5, 2009 -- also purportedly to put a satellite into orbit -- brought UN Security Council condemnation and tightened sanctions.

In response, Pyongyang staged a second nuclear test the following month.

A Security Council resolution approved later in 2009 bans the North from further nuclear tests or from launching a ballistic missile for any purpose.

The US-North Korean deal announced February 29 briefly raised hopes of progress in long-stalled six-nation nuclear disarmament efforts.

The North agreed to suspend its uranium enrichment programme, along with long-range missile launches and nuclear tests, in return for 240,000 tonnes of US food aid.

It insists a satellite launch is not a missile test. But the United States, Japan, Russia and other nations have called for it to scrap the plan, and even close ally China has expressed concern.

On Monday US State Department spokeswoman Victoria Nuland voiced hope the North would call off the launch, noting that the five other nations that had been involved in the six-party talks were united.

The State Department has told the North that any launch would be a "deal-breaker" for the food aid agreement.

Blast-off is timed to coincide with mass celebrations in North Korea marking the 100th anniversary of the birth of founding president Kim Il-Sung.

South Korea in strongly worded comments Monday accused its neighbour of trying to develop a nuclear-armed missile.

The North's news agency late that day said the blast-off would be a "historic occasion" for all Koreans and ridiculed the South's own two failed attempts to launch a satellite.