Prime Minister Tony Abbott has described Sydney siege gunman Man Haron Monis as someone with mental instability and an infatuation with extremism.

Speaking to media on Tuesday morning after the siege’s dramatic conclusion, Mr Abbott said it was tragic there were people in the Australian community who wanted to engage in politically motivated violence.

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“The perpetrator was well known to state and commonwealth authorities. He had a long history of violent crime, an infatuation with extremism, and mental instability,” Mr Abbott said.

“As the siege unfolded yesterday he sought to cloak his actions with the symbolism of the ISIL death cult”.

He commended New South Wales Premier Mike Baird for his “steadfastness” and Sydneysiders for being calm.

Hostages flee on Tuesday morning. Image: AAP

“There is nothing more Australian than dropping in at a local cafe for a morning coffee and it’s tragic that people going about their everyday business should have been caught up in such a tragic incident,” Mr Abbott said.

“These events do demonstrate that even a country as free, as generous, as safe as ours is vulnerable to acts of politically motivated violence”.

“They also remind us that Australia and Australians are resilient and ready to respond”.

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Cabinet’s national security committee has met again on Tuesday morning to review the situation, with the prime minister saying there would be a full investigation into what happened.

“Plainly, there are lessons to be learned and we will throughly examine this incident”.

Shorten ‘heartbroken’

Opposition Leader Bill Shorten said he and the PM were “partners when it comes to keeping Australians safe”.

“The loss of two innocent people in this horrific event overnight breaks our hearts,” Shorten said in a statement.

“We also keep in our thoughts the wounded and other hostages, and their families. Their ordeal is not over.

“Today, all of Australia stands with Sydney.”

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Speaking to media on Tuesday morning, Mr Shorten said he hoped a permanent memorial would be erected in Martin Place as a tribute to the victims.

The Labor leader said the attack had failed to divide Australians.

“It was a senseless act of violence, a crime designed to divide our country, but it has failed,” Mr Shorten said.

It has failed because I believe Australians have not lost faith and will never lose faith in our peaceful, multicultural society”.

“Together we will endure, together we will prevail”.