North Korea has announced a satellite launch barely two weeks after agreeing a deal with the US that Washington had greeted as a first step in resolving years of tension in the region.

Relations deteriorated sharply after Pyongyang's last such launch in 2009, which prompted UN security council condemnation and tightened sanctions. While North Korea said it was engaged in a peaceful space programme, others said it had breached resolutions against nuclear and ballistic missile activity.

The launch technology for missiles and satellites is near-identical, say experts. Pyongyang announced that the satellite would be launched between 12 and 16 April to mark the centenary of the birth of Kim Il-sung, the country's founder and grandfather of its leader, Kim Jong-un.

North Korea has promoted the anniversary as the point at which it emerges as a strong and prosperous nation. But strikingly it pledged "maximum transparency" and vowed not to affect neighbouring countries, in unusually emollient language.

"Legally, Pyongyang is within its rights to launch a satellite. But politically, this announcement is a slap in the face to the Americans," argued John Delury, a professor at Yonsei University. "If Pyongyang is serious about building a new relationship with the United States, they need to take concrete steps to demonstrate this is in fact a satellite launch, and that would include inviting monitors."

He noted that North Korea was launching the rocket from its west coast this time, suggesting it was seeking to minimise Japanese antagonism – although the newly built site is also thought to be more advanced than the last one.

State news agency KCNA said the launch of the indigenously developed Kwangmyongsong-3 "earth observation satellite" followed research "in line with the government's policy for space development and peaceful use", citing a spokesman for the Korean committee for space technology.

It will be launched by an Unha-3 rocket. The Unha-2 is better known outside the country as the Taepodong-2, a long-range missile. But last year the publication Jane's Strategic Weapons Systems said the Taepodong-3 might have been developed either to achieve a longer range or to launch satellites.

KCNA added: "A safe flight orbit has been chosen so that carrier rocket debris to be generated during the flight would not have any impact on neighbouring countries.

"The DPRK will strictly abide by relevant international regulations and usage concerning the launch of scientific and technological satellites for peaceful purposes and ensure maximum transparency, thereby contributing to promoting international trust and co-operation in the field of space scientific researches and satellite launches."

Japan's foreign ministry said the new launch would violate the security council resolution, according to the Jiji news service, while in Seoul, the unification ministry told AP it had no comment.

"They are trying to kill two birds with one stone – keeping North Koreans proud and elated while the US has no particular reason to protest since inspectors are going to be admitted to nuclear facilities [under the recent deal]," argued Leonid Petrov, lecturer in Korean studies at the University of Sydney.

"Of course it's a risky move, because technically they are violating the security council injunction, but it looks like they know what they are doing."

He suggested they might expect a reprimand but think they would be safe from more stringent action because the US was seeking to improve relations.

The agreement struck in Beijing last month saw North Korea agree to suspend nuclear missile tests and uranium enrichment, and submit to international monitoring, in return for substantial US food aid.

Hillary Clinton described the deal as a "modest first step".

Park Young-ho of the Korea Institute for National Unification in Seoul, a government-affiliated thinktank, told Reuters that the satellite announcement could be interpreted as "a means of applying pressure on the Americans in negotiations and a celebration of the founder's birth as well as an opportunity for the new leadership to celebrate the beginning of a new era".

Pyongyang hailed its 2009 test as a success, saying it had successfully launched a satellite broadcasting Song of General Kim Il-sung and Song of General Kim Jong-il.

But both US and South Korean officials said no satellite made it into orbit, although the rocket travelled twice as far, 1,900 miles, as previous tests had managed.

Barack Obama had issued a stern warning to Pyongyang not to proceed with that launch, and condemned it as an act of provocation which threatened nations "near and far".