The gunman who is holding an unknown number of people hostage at a Sydney café has been named as Man Haron Monis.

Monis, an Iranian native self-styled sheikh and spiritual healer, is well known to Australian authorities as he has had numerous encounters with police in recent years.

The 50-year-old Sydney man was sentenced to 300 hours of community service for sending offensive letters to the families of dead Australian soldiers between 2007 and 2009.

Earlier this year, he was arrested over the sexual assault of a woman which he allegedly committed during ''spiritual healing'' sessions.

He was then separately charged with more than 50 counts of indecent and sexual assault, according to The Sydney Morning Herald.

He was also charged in connection with the murder of his ex-wife, The Age newspaper reported.

His website, which has now been suspended, claims all charges moved against him are politically motivated.

It says he was a Shi'ite Muslim and later converted to Sunni Islam.

"I used to be a Rafidi [pejorative for Shi'ite], but not anymore. Now I am a Muslim," the website read.

On Monday morning (15 December) Monis allegedly stormed the Lindt Chocolat Cafe at Martin Place in central Sydney, taking numerous people hostage.

Five people have managed to escape since the crisis began more 14 hours ago.

Australian Prime Minister Tony Abbott said the gunman claimed to have a political motivation.

A tense stand-off with police is ongoing.

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