WASHINGTON (CBS News/CBSDC/AP) — The former deputy director of the CIA warns that the United States will see the kind of attack that is happening in Sydney, Australia, as a gunman who was previously arrested for extremist activity took several people hostage inside a café.

“What concerns me the most is that we are going to see this kind of terrorism around the world and we are going to see it here,” CBS News senior security contributor Mike Morell told “CBS This Morning.” “We are going to see this kind of attack here and we need to be prepared for that. It shouldn’t surprise people when this happens here sometime over the next year or so, guaranteed.”

A gunman took several people hostage Monday at the Lindt Chocolate Café in downtown Sydney. Ten Eyewitness News, a CBS News partner, reports that the gunman wants an ISIS flag delivered to the café and that he also wants to speak directly to Australian Prime Minister Tony Abbott.

Morell said that this type of attack is “very difficult to prevent.”

“It’s very difficult to stop something like this. One way this happens is if ISIS leadership directs it and intelligence agencies can often see that and prevent that. If people are vocal about what they’re going to do on social media you can prevent it. But if they’re quiet about it, it’s very easy to carry out something like this,” Morell said on “CBS This Morning.”

Morell added that ISIS has had its sights set on Australia for backing the West.

“ISIS has had a focus on Australia for some time. Some 300 Australians have gone to the Middle East to fight in that war – 70 or so are fighting for ISIS,” Morell explained. “Just a couple months ago, the Australians did a country-wide raid, arresting a number of people after a senior ISIS leader called for individuals in Australia to behead Australians in public for ISIS. There is this focus on Australia.”

Five hostages have so far fled the café.

Hundreds of police flooded into the area, streets were closed and offices evacuated. The public was told to stay away from Martin Place, home to the state premier’s office, the Reserve Bank of Australia, and the headquarters of two of the nation’s largest banks. The state parliament house is a few blocks away. The U.S. consulate is also nearby.

“We have advised U.S. citizens and others avoid the area around Martin Place until further notice,” U.S. State Department spokeswoman Jen Psaki said in a written statement. “The U.S. Consulate General in Sydney has been evacuated, along with other buildings in the vicinity of Martin Place, as a security precaution. A small group of Consulate staff continues to work from a secure location.”

Television footage shot through the cafe’s windows showed several people with their arms in the air and hands pressed against the glass, and two people holding up a black flag with the Shahada, or Islamic declaration of faith, written on it.

The Shahada translates as “There is no God but Allah and Muhammad is His messenger.” It is considered the first of Islam’s five pillars of faith, and is similar to the Lord’s Prayer in Christianity. It is pervasive throughout Islamic culture, including the green flag of Saudi Arabia. Jihadis have expropriated the Shahada in their own black flag.

Heavily armed officers were lined up outside the cafe, and a man with a backpack inside the cafe could be seen walking back and forth in front of the glass doors.

“Police have been in attendance and have controlled the situation from very early this morning,” said Scipione, the police commissioner. “We are at this stage continuing to secure and make sure that we are doing all we can to bring this to a peaceful outcome.”

Abbott said the National Security Committee of Cabinet met to be briefed on the situation.

“The whole point of politically motivated violence is to scare people out of being themselves,” Abbott said. “Australia is a peaceful, open and generous society – nothing should ever change that. And that’s why I would urge all Australians today to go about their business as usual.”

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