A gunman holding about 15 hostages in a Sydney cafe is a fringe radical with a criminal record, news reports say.

The 49-year-old named Man Haron Monis came to Australia as a refugee from Iran in 1996, The Australian newspaper reports.

The man reportedly came to police attention after he was charged with sending offensive letters to the families of Australian soldiers killed in Afghanistan.

The newspaper says he is currently on bail awaiting trial after he was charged with being an accessory to the murder of his ex-wife and in 40 indecent assaults. SAPA