A near two-week launch window for a North Korean long-range rocket began Monday, a day after Pyongyang said it may delay liftoff.
North Korea has faced mounting international pressure to abandon what critics call a cover for a banned missile test.
Scientists had been pushing forward with final preparations for the launch from a west coast site but are considering "readjusting" the timing for unspecified reasons, an unidentified spokesman for the Korean Committee for Space Technology told North Korea's state-run Korean Central News Agency early Sunday.
It was unclear whether diplomatic intervention or technical glitches were behind the potential delay. A brief KCNA dispatch said scientists and technicians were discussing whether to set new launch dates but did not elaborate.
North Korea's state media has yet to follow up on Sunday's announcement.
North Korea announced earlier this month that it would launch a three-stage rocket mounted with a satellite from the Sohae station on its northwest coast sometime between Monday and December 22. Pyongyang calls it a peaceful bid to send an observation satellite into space, its second attempt this year. An April launch failed seconds after liftoff.
Word of a possible delay came just days after satellite photos indicated that snow may have slowed launch preparations, and as officials in Washington, Seoul, Tokyo, Moscow and elsewhere urged North Korea to cancel a liftoff widely seen as a violation of bans against missile and nuclear activity because the rocket shares the same technology used for firing a long-range missile.
Commercial satellite imagery taken by GeoEye on December 4 and shared Friday with The Associated Press by the 38 North and North Korea Tech websites showed the Sohae site northwest of Pyongyang covered with snow. The road from the main assembly building to the launch pad showed no fresh tracks, indicating that the snowfall may have stalled the preparations.
However, analysts believed rocket preparations would have been completed on time for liftoff as early as Monday.
Some South Korean media, citing unidentified government sources in Seoul, speculated Monday that North Korea was facing unspecified technical problems. The Korean Peninsula has seen a string of snowstorms and frigid days.
A rocket can be launched during a snowfall, but lightning, strong wind and freezing temperatures could stall a liftoff, said Lee Chang-jin, an aerospace professor at Seoul's Konkuk University.
The launch announcement captured global headlines because of its timing: South Korea and Japan hold key elections this month, President Barack Obama begins his second term next month and China has just formed a new leadership. North Koreans also have begun a mourning period for late leader Kim Jong Il, who died on December 17, 2011.
Last week, US Secretary of State Hillary Rodham Clinton said Washington was deeply concerned about the launch, and urged foreign ministers from NATO and Russia to demand that Pyongyang cancel its plans.
North Korea has unveiled missiles designed to target U.S. soil and has tested two atomic bombs in recent years, but has not shown yet that it has mastered the technology for mounting a nuclear warhead to a long-range missile. Six-nation negotiations to offer North Korea much-needed aid in exchange for nuclear disarmament have been stalled since early 2009.
China, the North's main ally and aid provider, noted its concern after North Korea declared its latest launch plans. It acknowledged North Korea's right to develop its space program but said that had to be harmonized with restrictions including those set by the U.N. Security Council.
In Seoul, officials at the Defense Ministry, Joint Chiefs of Staff and the Foreign Ministry said they couldn't immediately determine what might be behind the possible delay.
North Korea may hold off if Washington actively engages Pyongyang in dialogue and promises to ship stalled food assistance to the country, said Koh Yu-hwan, a professor of North Korean studies at Seoul's Dongguk University.
In February, Washington agreed to provide 240,000 metric tons of food aid to North Korea in exchange for a freeze in nuclear and missile activities. The deal collapsed after North Korea attempted its April launch.
Analyst Baek Seung-joo of the South Korean state-run Korea Institute for Defense Analyses in Seoul said China must have sent a "very strong" message calling for the North to cancel the launch plans.
A successful launch means North Korea could develop an intercontinental ballistic missile capable of striking the US mainland within two to three years, though the country would need many more years to acquire the technology to arm the missile with a nuclear warhead, said Chong Chol-Ho, a weapons of mass destruction expert at the private Sejong Institute near Seoul.