SEOUL, South Korea >> North Korea on Monday extended the launch period for a controversial long-range rocket by another week until Dec. 29, citing technical problems.

An unidentified spokesman for the North’s Korean Committee of Space Technology told state media that scientists found a “technical deficiency in the first-stage control engine module of the rocket.” The statement didn’t elaborate but said technicians were “pushing forward” with final preparations for the launch.

North Korea is making its second attempt of the year to launch a rocket that the United Nations, Washington, Seoul and others call a cover meant to test technology for missiles that could be used to strike the United States. They have warned North Korea to cancel the launch or face a new wave of sanctions.

The North Koreans call the launch a peaceful bid to advance their space program, and a last wish of late leader Kim Jong Il, who died a year ago, on Dec. 17. North Korea is also celebrating the centennial this year of the birth of national founder Kim Il Sung, current leader Kim Jong Un’s grandfather. An April launch broke apart seconds after liftoff.

The announcement of the planned rocket launch has sparked worry because of the timing: South Korea and Japan hold key elections this month, President Barack Obama begins his second term in January, and China has just formed a new leadership.

The North had originally set up a 13-day launch window, starting Monday, but it announced early Sunday that it may delay the liftoff because of unspecified reasons.

Experts in Seoul and Tokyo had speculated that technical glitches may have forced scientists to postpone the launch of the finicky three-stage rocket, its fifth attempt since 1998.

Temperatures in the border city of Sinuiju, near the launch site, dropped to minus-13 C (8.6 F) on Monday morning, and the Korean Peninsula has been seized by early winter storms and unusually cold weather, the Korea Meteorological Administration said in Seoul.

Engineers can launch a rocket when it’s snowing, but lightning, strong wind and freezing temperatures have the potential to stall liftoff, said Lee Chang-jin, an aerospace professor at Seoul’s Konkuk University.

Snow covered the North’s launch site last week, according to commercial satellite imagery taken by GeoEye on Dec. 4 and shared with The Associated Press by the 38 North and North Korea Tech websites. The road from the main assembly building to the launch pad showed no fresh tracks, indicating that the snowfall may have stalled the preparations.

Still, Japanese Prime Minister Yoshihiko Noda said Monday that his government would maintain vigilance. Tokyo has mobilized its military to intercept any debris from the rocket.

“At this moment, we are keeping our guard up,” Defense Minister Satoshi Morimoto told reporters Monday. “We have not seen any objective indication that would cause us to make any change to our preparedness.”

At least one Aegis-equipped South Korean destroyer has been deployed in the Yellow Sea to monitor North Korea’s rocket launch, according to South Korean officials.

The United States has also moved extra ships with ballistic missile defense capabilities toward the region, officials said.

The U.S., Japan and South Korea say they’ll seek U.N. Security Council action if the launch goes ahead in defiance of existing resolutions. The council condemned April’s launch and ordered seizure of assets of three North Korean state companies linked to financing, exporting and procuring weapons and missile technology.

In addition to four failed launches, North Korea has unveiled missiles designed to target U.S. soil and has tested two atomic devices in recent years. It has not yet proven to have mastered the technology for mounting a nuclear warhead to a long-range missile, however.

A successful launch would mean North Korea could develop an intercontinental ballistic missile capable of striking the U.S. mainland within two to three years, said Chong Chol-Ho, a weapons of mass destruction expert at the private Sejong Institute near Seoul.

Six-nation negotiations to offer North Korea much-needed aid in exchange for nuclear disarmament have been stalled since early 2009.

Last week, U.S. Secretary of State Hillary Rodham Clinton said Washington was deeply concerned, and urged foreign ministers from NATO and Russia to demand that Pyongyang cancel its plans. Moscow joined calls on Pyongyang to reconsider.

China, North Korea’s main ally and aid provider, also noted its concern, acknowledging North Korea’s right to develop its space program but urging Pyongyang to harmonize the bid with restrictions — including those set by the U.N. Security Council.

International pressure and the prospect of dialogue may be a factor in the delay, analysts in Seoul said.

China must have sent a “very strong” message calling for the North to cancel the launch plans, said analyst Baek Seung-joo of the South Korean state-run Korea Institute for Defense Analyses.

North Korea may also be holding off if the U.S., its longtime Korean War foe, actively engages Pyongyang in dialogue, said Koh Yu-hwan, a professor of North Korean studies at Seoul’s Dongguk University.

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Associated Press writer Mari Yamaguchi contributed to this report from Tokyo.