North Korea moved up the window of its planned long-range rocket launch to as early as Sunday in defiance of outside governments who suspect a banned test of ballistic missile technology, South Korea’s Defense Ministry said Saturday.

North Korea, which says it will attempt to place a satellite in orbit, informed the International Maritime Organization it moved up the launch window from Feb. 8-25 to Feb. 7-14, Japan’s Kyodo News Service reported. No reason was given for the change.

While the North claims such efforts are a benign attempt to develop the capability for putting satellites into space, outside governments say it is a cover for testing ballistic missiles. That move would constitute yet another major violation of U.N. Security Council resolutions banning Pyongyang from carrying out any nuclear or ballistic missile tests.

Notifications to the International Maritime Organization are intended to alert seagoing traffic that might be in the area. North Korea did not inform international organizations of any other changes in its plan, and the rocket’s expected flight path remains the same, said South Korean Defense Ministry spokesman Moon Sang Gyun.

Recent commercial satellite imagery analyzed by U.S. researchers showed tanker trucks at the launch pad at North Korea’s Sohae facility, which likely indicates the filling of fuel and oxidizer tanks in preparation for the launch, the Associated Press reported. It is not yet clear if a rocket is on the launch pad yet, according to the North Korea-focused 38 North website.

An official from the Korea Meteorological Administration, South Korea’s weather agency, said rain or snow is expected in the North Korean region where the launch pad is located Monday, Thursday and next Saturday. He spoke on condition of anonymity, citing office rules, the AP reported.

The revised plan comes weeks after North Korea conducted its fourth nuclear test. International governments worry nuclear tests and long-range missile launches signal the North is getting closer to creating a nuclear warhead small enough to fit on an intercontinental missile capable of reaching targets as far away as the U.S. West Coast.

North Korea tested nuclear explosive devices in 2006, 2009 and 2013, and claimed it successfully delivered a satellite into orbit in December 2012, the last time it launched a long-range rocket.

South Korean analysts speculate the secretive North Korean leadership, which is sensitive to symbolic gestures, might be trying to pull off the launch ahead of Feb. 16, the birthday of late dictator Kim Jong Il, the father of current leader Kim Jong Un.

The South Korean defense ministry said Seoul and the U.S. are deploying key military assets, including the South’s Aegis-equipped destroyers and radar spy planes, to track the North Korean rocket after its launch. The U.S. stations more than 28,000 troops in the South as a buttress against North Korean aggression.

The Seoul government said it will stay on full alert for the possible launch, South Korea’s Yonhap news agency reported.

Pyongyang’s announcement prompted Japan’s Foreign Ministry to set up an emergency response desk to monitor and prepare for the launch. Japan deployed Patriot missile batteries in Tokyo and on the southern island of Okinawa to shoot down any debris from the rocket that might threaten to fall on its territory.

The United States and South Korea are likely to respond to any launch with a call for tighter sanctions in North Korea.

China, North Korea’s only major ally, is unlikely to support stronger punishment over concerns it could provoke a regime collapse and send a stream of refugees across the border, analysts say. China is responsible for about 70% of the North’s trade volume, according to South Korean estimates.