North Korea's preparations for a planned rocket launch that has triggered international condemnation and sanctions threats may have been delayed by heavy snow, a US think tank said Friday.

Analysis of fresh satellite imagery suggests preparations at the Sohae satellite launch station are proceeding "more slowly than previously reported," the US-Korea Institute at Johns Hopkins University said.

Pyongyang announced last week that it would launch a rocket -- ostensibly aimed at placing a satellite in orbit -- between December 10 and 22.

"Since this is Pyongyang's first attempt to launch a long-range rocket in winter, weather may be a new factor," Nick Hansen, an expert on imagery analysis, wrote on the institute's website 38 North.

Recent images taken on December 4 showed no tracks in heavy snow that had fallen on the launch site the day before, suggesting at least a temporary halt in operations, Hansen said.

This would raise doubts over South Korean media reports on Wednesday -- citing government sources -- that the North had completed installing all three stages of the Unha-3 rocket on the launch pad.

Hansen noted that the 12-day launch window announced by Pyongyang was more than twice as long as the five-day window given to its last rocket launch bid in April, which ended in failure.

"This may indicate that the North is well aware of the potential pitfalls caused by bad weather and has built flexibility into the launch schedule," he said.

The United States and its key Asian military allies, South Korea and Japan, insist the launch is a disguised ballistic missile test that violates UN resolutions triggered by Pyongyang's two nuclear tests in 2006 and 2009.

S. Korea urges North to spend on debt, not missiles
Seoul (AFP) Dec 7, 2012 - South Korea on Friday urged North Korea to repay millions of dollars in debt related to past food aid, and slammed the regime in Pyongyang for squandering scant resources on long-range missile tests.

The South provided the North with some 2.6 million tonnes of food worth $720 million in six installments between 2000 and 2007.

The food aid was provided in the form of a cheap loan, with repayments to be made over 20 years. The first installment of $5.83 million was due in June but was never paid, the Unification Ministry said.

Ministry spokesman Kim Hyung-Suk said Seoul's state-run Export-Import Bank had sent a message to North Korea's Foreign Trade Bank, warning that delay penalties would be charged.

"Without repaying the debt, the North's leadership plans to launch a missile at a time when its people are suffering from food shortages," Kim told reporters.

"It is wasting money that could feed its people for several years."

North Korea has announced plans to launch a long-range rocket -- ostensibly aimed at placing a satellite in orbit -- between December 10 and 22.

The United States and its key Asian military allies, South Korea and Japan, insist the launch is a disguised ballistic missile test that violates UN resolutions triggered by Pyongyang's two nuclear tests in 2006 and 2009.

In a report published Thursday, the unification ministry estimated that the North had spent $1.3 billion dollars on it's long-range missile programme in 2012.

As well as food aid, the South has also lent the North equipment and materials worth $140 million for railways and roads, and another $88 million for developing light industry and natural resources.

The food and fertiliser aid ended after President Lee Myung-Bak took office in early 2008 and rolled back the "sunshine" policy of aid and engagement with the North.