Australians take to Twitter to support Muslims

Twitter users used the hashtag #IllRideWithYou to pledge their support for Australian Muslims on Monday after an Islamic extremist held hostages in a Sydney cafe.

The hashtag had been mentioned more than 90,000 times by Monday afternoon.

The siege, which lasted for more than 15 hours, spurred fears that the incident might produce retaliatory violence against Muslims.

Australians offered to travel with Muslim Australians who feared they might be targeted because of their religious affiliations.

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"If you reg take the #373 bus b/w Coogee/MartinPl, wear religious attire, & don't feel safe alone: I'll ride with you. @ me for schedule," one Twitter user posted.

Australian Muslim leaders released a statement condemning the event, calling it a "despicable act."

Quilliam Foundation, a counter-extremism think tank, has been warned of increased jihadist attacks for for the past few years.

"[I]t's just the beginning for Australia in what could well be a number of attacks in the region," said Hara Rafiq, head of outreach at Quilliam Foundation. "This is something indicative to what we have coming."

The siege should serve as a warning to to the rest of the world," Rafiq told CNBC in a phone interview Monday. "Australia, in particular, has the worst problem of Jihadi foreign fighters in the U.K., per capita."

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The alleged gunman, Shiekh Haron, had not been linked have any direct links to ISIL, but he's linked to "their ideology that allows him to kill other people, be their Muslims or non-Muslims, to affect political change," Rafiq noted.