"It is my pleasure to inform you of the decision of the government of the Democratic People's Republic of Korea (DPRK) to launch earth observation satellite 'Kwangmyongsong' pursuant to the national space development program," Jon Ki-chol, director-general of the North's Maritime Administration, said in the letter.

Japan's Kyodo News reported earlier that the North's posts and telecommunications minister, Kim Kwang-chol, also sent a similar notice to the International Telecommunication Union (ITU), saying the satellite will be the Kwangmyongsong type and have a four-year operational life.

It is required for countries to give international organizations advance notice of rocket launch plans to warn planes and ships to stay away from the areas to be affected by launches.

Pyongyang has done so in its previous rocket launches.

According to the coordinates the North provided, the rocket's first stage is expected to fall in the West Sea, the fairing in the East China Sea and the second stage in the Philippine Sea.

Satellite imagery has shown increased activities at the North's Sohae rocket launch site, also known as Dongchang-ri, sparking concern that Pyongyang may be preparing for a test just a few weeks after its fourth nuclear detonation.

Monday's notices to the U.N. agencies confirmed the concern.

The United States warned of tough responses if Pyongyang forges ahead with a launch.

"This argues even more strongly for action by the U.N. Security Council and the international community to impose real consequences for the destabilizing action that the DPRK has taken, is taking, and to raise the cost to the leaders through the imposition of tough additional sanctions," Assistant Secretary of State Daniel Russel told reporters, according to news reports.

State Department spokesman John Kirby said that a satellite launch would violate numerous Security Council resolutions as it utilizes proscribed ballistic missile technolgy.

"This latest announcement further underscores the need for the international community to send the North Koreans a swift, firm message that its disregard for U.N. Security Council resolutions will not be tolerated," Kirby said at a regular briefing.

South Korea's presidential spokesman, Jeong Yeon-guk, said the country is keeping a close watch over North Korea while taking necessary measures to cope with the situation.

A new rocket launch would represent blatant defiance of the international community, including the U.N. Security Council, which has been working on fresh sanctions to punish the regime for its Jan. 6 nuclear test.

North Korea says its rocket launches are aimed at putting satellites into orbit, claiming it has the right to the peaceful use of space. But Pyongyang is banned from such launches under U.N.

Security Council resolutions as it has been accused of using them as a cover for testing intercontinental ballistic missiles (ICBMs).

Experts say long-range rockets and ICBMs are basically the same with differences only in payloads.

The North's missile program has long been a key security concern in the region and beyond.

Pyongyang is believed to have developed advanced long-range ballistic missile technologies through a series of test launches, including the most recent launch in 2012, in which the North succeeded in putting a satellite into orbit.

That test sparked fears that the North has moved closer to ultimately developing nuclear-tipped missiles that could potentially reach the mainland United States. The country has so far conducted four underground nuclear tests, in 2006, 2009, 2013 and last month. (Yonhap)