Rumors that North Korean leader Kim Jong Un was assassinated have been shot down by US officials.

The claim originated in China on Friday and rapidly circulated on Twitter and Chinese micro-blogging sites.

Due to the difficulty of verifying news from the ultra-secretive government of North Korea, news organizations were unable to debunk the rumor.

But U.S. officials said that they believed the claim to be untrue, and had seen no evidence of “abnormal activity” in North Korea.

The claim that Kim Jong Un, supreme leader of North Korea since the death of his father Kim Jong Il in December, had died apparently stemmed from a message sent out by a man who works near the country’s embassy in Beijing.

The man posted on Sina Weibo: “Downstairs from the office, the cars at the Korean embassy are increasing rapidly, now there are over 30 cars. It’s the first time I’ve seen this situation, did something happen in Korea?”

This seemingly innocuous question, bolstered by other witnesses who saw an unusual number of cars at the embassy, was magnified by the power of internet gossip into a rumor that Kim Jong Un had been assassinated by gunmen who burst in his bedroom and were subsequently killed by his bodyguards.

The claim that Kim Jong Un had died apparently stemmed from a message sent out by a man who works near the country's embassy in Beijing

Wilder commentators even spun the supposed assassination in to a broader claim that a coup was underway in North Korea which could depose the Kim dynasty, rulers of the country ever since it split with the south in 1948.

But when ABC News asked U.S. officials for confirmation of the assassination rumors, one simply told them: “There’s nothing to this.”

Another official said: “Our experts are monitoring the situation and we see no abnormal activity on the [Korean] peninsula and nothing that credits that tweet as accurate.”

It was thought that the death of the elder Kim would herald a period of instability, potentially leading to regime change, but those expectations have not been fulfilled.

A less dramatic but equally bizarre explanation for the large number of cars at the North Korean embassy was suggested by Gawker and Chinese news agency Phoenix.

They pointed out that this month would have been the 70th birthday of Kim Jong Il, and a large number of events including tours of China and North Korea are set to mark the anniversary.

So perhaps the increased activity at the embassy was not to do with the current leader, but with his dead father – in fact, it is not even clear whether or not Kim Jong Un is currently in China.

The escalating pace of rumors points to the speed at which false information can speed round the world via social networks and online news sources.

It also highlights the increasing importance of Chinese micro-blogs, known as weibo, which are more lightly regulated than other Chinese media.

Weibo and Twitter seem to have fed off each other in the case of the Kim Jong Un rumors, as most tweets about the claims pointed to weibo as their sources, while Chinese posts frequently mentioned Twitter to back up their own accuracy.