SEOUL (Reuters) - Hackers have attacked North Korea’s official Youtube and Twitter accounts, posting a cartoon showing Kim Jong-il’s heir apparent driving a sports car into a crowd of starving countrymen.

The cyber attack on Saturday, believed to be leader-in-waiting Kim Jong-un’s birthday, also called for an uprising against the communist nation’s ruling dynasty.

The online embarrassment comes at a time when North Korea has called for dialogue with South Korea to defuse tensions aggravated by an exchange of artillery fire and the sinking of a South navy ship last year.

One of the messages posted on the North’s official Twitter account said the ailing Kim Jong-il and his son were sworn enemies.

Another called for the removal of Kim Jong-il for hosting drinking parties at his lavish cottage while 3 million countrymen starved to death.

Several people on a South Korean internet forum, Dcinside, claimed responsibility for the attack.

A two-minute spoof posted on the North’s official youtube account showed Kim Jong-un running over a group of starving people and a train, laden with birthday gifts for him, derailed after hitting children on the tracks.

The Youtube account is often used by the North to communicate with the outside world.

There was no immediate comment from the North on the cyber attack. The North Korea’s official mouthpiece, KCNA news agency, also did not report any public events or festivals to mark Kim Jong-un’s birthday.

Very little is known about Kim Jong-un outside North Korea, who is the youngest son of Kim Jong-il.