Lawyers who defended the Sydney siege gunman on a string of charges and the magistrate who bailed him have received deaths threats, officials said Friday, amid growing anger that he was on the streets.

Iranian-born Man Haron Monis, a self-styled Islamic cleric, took 17 people hostage at a cafe in the heart of the city's financial district on Monday.

The 50-year-old was killed along with two victims -- the cafe's manager, 34, and a 38-year-old mother-of-three -- in a bloody end to the standoff.

Known to authorities for his extremist views, Monis was on bail at the time for various charges, including sexual offences and abetting the murder of his ex-wife.

Prime Minister Tony Abbott has ordered an urgent enquiry amid mounting criticism that authorities failed to protect the public, with the backlash extending to the magistrate who released Monis and lawyers who represented him.

"To make death threats as has been done against members of the profession for doing a job is really an unfortunate reaction," New South Wales Bar Association president Jane Needham told ABC radio.

She said the reaction was "understandable but wrong-headed", without detailing the nature of the threats.

"The jobs of the judiciary are very difficult, they're very complex and magistrates in particular deal with many cases which come before them and they have to make their decisions on the basis of what is before them at the time and the operation of the law.

"As to the lawyers, it's very important to remember that lawyers are just doing their job," she added.

One of the hostages killed, Katrina Dawson, was a barrister and the cafe where she died was a favourite of many in the legal profession.

"There is a lot of distress," Needham said of the Bar Association.

"The Lindt cafe was a centre of people's lives here and there is a real feeling, additional to the grief and shock and fear, (that) it could have been anyone."
The review Abbott has ordered will examine Monis' arrival in Australia from Iran in 1996, the decision to grant him asylum and citizenship, what information agencies had about him and how it was shared.

It will also ask how he managed to get a gun and how he could claim welfare benefits for years despite apparently being able-bodied.

Security across Sydney has been stepped up since the siege with police late Thursday searching several properties across the city, reportedly as part of a ongoing counter-terrorism investigation.

Officials said the raids were unconnected to Monis or the Sydney tragedy.