Counter terrorism police have contacted Sydney man and onetime terror accused Zaky Mallah and asked him for an ISIS flag.

Just over four hours into the Martin Place siege, officers the NSW Police Joint Counter Terrorism Team and asked him if he could give them an ISIS flag.

Zaky Mallah, 30, from Westmead in western Sydney offered the Counter Terrorist police the flag that hangs on the wall of his apartment, the moderate Islamic Front flag, but 'they weren't interested'.

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Counter terrorism police contacted Zaky Mallah four hours into the Martin Place siege and requested an ISIS flag. He offered his Islamic Front flag (pictured, on the wall behind Mr Mallah) but police weren't interested

Flag request: Counter terrorism police contacted Zaky Mallah and asked him for an ISIS flag, which he didn't have

Counter terrorism police made the request to Zaky Mallah as officers staked out the Lindt cafe in Martin Place (pictured) as the siege entered its fifth hour

The news comes as Radio 2GB broadcaster Ray Hadley said he had three telephone conversations with a young man who is among the hostages and that the hostage said the gunman had made several demands.

Earlier, the gunman appeared to force the hostages to hold up another Islamic flag, the Shahada which bears the words in Arabic, 'There is no God but Allah'.

Mr Mallah, once accused of terrorism but acquitted, has turned against extremists since a visit to Syria

Mr Mallah was the first person to be charged with terrorism back in 2003 after he made a video which Federal Police and ASIO said contained a planned suicide attack on federal government offices in Sydney.

Mallah, a Lebanese Australian, was charged under Australia's then new anti-terrorism laws after he made the video.

He spent two years in the high maximum security Multi Purpose Unit at Goulburn prison awaiting trial, before being acquitted. It was only in 2009 that he was able to obtain an Australian passport.

Two years ago Mr Mallah travelled to Syria and lived with the FSA rebels engaged in the bloody civil war against Muslim hardliner President Bashar el Assad 'before it got crazy over there'.

After returning home, he encouraged young people to go to Syria and engage in jihad to experience the freedom fight taken up against El Assad, but since the rise of ISIS and Jabhat al-Nusra he has changed his mind.