By James Pearson

SEOUL (Reuters) - An international media frenzy over reports that North Korean leader Kim Jong Un's uncle had been executed by throwing him to a pack of dogs appears to have originated as satire on a Chinese microblogging website.

The story, which spread like wildfire after it was picked up by a Hong Kong-based newspaper, has created an image that Pyongyang's young ruler is even more brutal and unpredictable than previously believed.

While North Korea has said it purged and executed Kim's uncle, Jang Song Thaek, last month, it did not release details of how the man who was once the second most powerful figure in the isolated country was killed.

Initial speculation was that Jang had been killed by firing squad, a fate that media outlets said was the usual one reserved for "traitors". But an alternative narrative of the 67-year old's death emerged on what appears to have been a satirical post on the Chinese Tencent Weibo site that has been repeated by many media outlets worldwide.

The December 11 post on Tencent Weibo (http://t.qq.com/p/t/312572016688539) said Jang and five aides were killed by dogs.

The post records that it was viewed 290,000 times.

The Hong Kong-based Wen Wei Po newspaper released an article and a screenshot of the Weibo post which it used to justify its report that Jang had been torn apart.

Wen Wei Po, although independent, is viewed as being pro-Beijing. Its report was in turn picked up 12 days later by the Singapore-based Straits Times and then by a wide range of U.S. and European media from print to television.

Kim Jong Un, believed to be around 30 years old, has been in power for two years and presided over a nuclear test and two rocket test launches that are banned under United Nations sanctions.

In 2013, Pyongyang threatened to strike South Korea, the United States and Japan in fiery rhetoric that triggered an arms buildup in East Asia.

One of the pitfalls of reporting on North Korea is that few independent media have offices there and visiting media are tightly controlled in a country which ranks among the lowest in global surveys of press freedom.

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Because of the lack of first hand information, many lurid stories about the country gain credence.

Trevor Powell, a Chicago-based software engineer, who first spotted the link to the Weibo post and reported it on his own blog said that analysts and experts were "still all missing the obvious fact that the original source of the Wen Wei Po story was a tweet from a known satirist or someone posing as him/her."

Powell blogged about the post at http://trevorpowell.com/2014/01/04/120-dogs-chinese-satirists-tweet-takes-all-english-news-media-for-a-ride/.

He could not immediately be reached for comment.

Officials at Wen Wei Po declined to comment on the article.

(Additional reporting by James Pomfret and Yimou Lee in HONG KONG and John Ruwitch in SHANGHAI. Editing by Raju Gopalakrishnan)