South Korea said Thursday it has detected preparations by rival North Korea to fire a long-range rocket and warned that Seoul will shoot down any rocket parts flying over South Korean territory.

North Korea told international organizations Tuesday that it will launch an observation satellite aboard a rocket between Feb. 8 and 25. South Korea, the United States and others call the plans a cover for a banned test of a missile that could strike the U.S. mainland.

The launch announcement follows an outpouring of global condemnation over the North's fourth nuclear test on Jan. 6. Seoul and Washington have also denounced the rocket launch plan, but if North Korea's past patterns are any clue, angry warnings probably won't dissuade a coming launch.

South Korean defense officials said Thursday that the North is pushing ahead with the launch plans at its Tongchang-ri launch site on its west coast. They refused to provide details because they said they involve confidential intelligence on the North.

Recent commercial satellite images showed an increased number of vehicles at North Korea's Sohae launch station on Feb. 1, compared to a week earlier. This suggests that the North is preparing for a space launch in coming weeks, according to 38 North, a North Korea-focused website run by the U.S-Korea Institute at Johns Hopkins School of Advanced International Studies.

However, the website said it was impossible to tell from the satellite imagery whether a space launch vehicle was present.

South Korean and U.S. officials said a launch would threaten regional security and violate U.N. Security Council resolutions that ban the North from engaging in any nuclear and ballistic activities.

Diplomats at the U.N. Security Council have already pledged to pursue fresh sanctions on North Korea over its recent nuclear test.

South Korea's president on Thursday called for strong U.N. sanctions that will make North Korea realize it cannot survive if it does not abandon its weapons programs.

There are questions, however, over whether any sanctions will force real change in the North because China, the North's last major ally and a veto-wielding U.N. Security Council member, is reluctant to join in any harsh punishment against the North.

Beijing on Wednesday urged restraint over North Korea's announcement of its launch plans, and expressed skepticism over the U.S. calls for tough new sanctions.

U.N. Secretary-General Ban Ki-moon, a former South Korean foreign minister, said the announcement "will further aggravate the profound concerns that the international community already has in the wake of the recent nuclear test," a spokesman said.

In South Korea and Japan, there are fears about falling debris, although nothing landed in their territories during the North's most recent launches. Seoul officials estimated the first stage of the rocket would fall off the west coast of South Korea, more debris would land near the South's Jeju Island, and the second stage would land off the Philippines' east coast.

Moon Sang Gyun, a spokesman at Seoul's Defense Ministry, said Thursday that South Korea would fire missiles to intercept any fragments of the North's rocket if they threaten to fall on its territories. Seoul issued similar plans before the North's previous rocket launches in recent years.

North Korea has spent decades trying to develop operational nuclear weapons along with missiles capable of striking the mainland United States.

North Korea's last long-range rocket launch, in December 2012, was seen as having successfully put the country's first satellite into orbit after a string of failures. Each new rocket launch improves North Korea's missile technology, which is crucial for its goal of developing a nuclear-armed missile capable of hitting the U.S. mainland.

North Korea, an autocracy run by the same family since 1948, is estimated to have a handful of crude nuclear devices and an impressive array of short- and medium-range missiles, but it closely guards details about its nuclear and missile programs. This means there is considerable debate about whether it can produce nuclear bombs small enough to place on a missile, or missiles that can reliably deliver their bombs to faraway targets.