Monis was a terrorist, argues Stratfor

A US expert has no doubt the Sydney cafe siege had its roots in terrorism, even though it was carried out by a "bumbling Kramer".

Scott Stewart, a security analyst with intelligence group Stratfor, says it's "intent" that separates terrorism from the sole act of a violent or mentally unstable person.

Despite any personal, legal or mental issues hostage-taker, Man Haron Monis, may have had, he clearly intended the siege to be an "act of terrorist theatre", he adds.

Monis, 50, took 18 people hostage inside the popular Lindt cafe at Martin Place in Sydney's CBD on Monday.

The siege lasted 16 hours and ended in the early hours of Tuesday with the deaths of two hostages, and Monis.

Mr Stewart believes Monis' motives were clear from the headband he wore and the banner he made the hostages hold up in the cafe window.

The banner displayed the Muslim statement of faith while the headband indicated Monis was a solder of Mohammad. Both items have been appropriated by Islamic State and other terror groups.

Some commentators have argued Monis actions didn't amount to terrorism because his plan was amateurish, he acted alone and had no connections to terrorists outside Australia.

"But just because Monis was more of a bumbling Kramer than a deadly Carlos the Jackal does not mean he was not a grassroots terrorist operatives," Mr Stewart said in an analysis of the siege released on Friday.

Most grassroots operatives tended to be more like "stray mutts" than lone wolves.

"Government resources are too limited to monitor the activities of each of them," Mr Stewart said.