Local residents and University of Iowa students celebrated Sunday night after learning United States troops had killed Al Qaeda leader Osama bin Laden, the mastermind behind the 9/11 terrorist attacks.

Many learned through social networking site that President Obama would make an impromptu address to the nation regarding a national-security issue, prompting many to turn on their TVs.

Those across the world then heard Obama say that after nearly a decade, the U.S. military launched a "targeted attack" Sunday on a compound in Pakistan that had killed bin Laden.

"On nights like this one, we can say to the families who have lost loved ones to Al Qaeda’s terror, justice has been done," Obama told Americans.

Many University of Iowa students went out downtown to celebrate — some screaming chants, carrying flags, and wearing American-theme jackets. The scene showcased firecrackers and honking cars.

"No other country can do this because we’re No. 1," said UI junior Kristianne Stenoien with a cheer.

This type of joyous reaction was on display throughout the world Sunday night and into early Monday morning.

Cameras flashed as television crews captured gleeful crowds chanting and cheering outside the White House gates while, in New York City, masses flooded Ground Zero. Social networking sites such as Facebook and Twitter buzzed — "Osama Bin Laden" and other related phrases were high among Twitter’s trending topics Sunday night. A number of students said they found out about bin Laden’s death through Facebook.

Studying in the Main Library, UI junior Audra Gahn said she found the announcement "kind of scary" and said she thinks it’s something that’s going to "cause consequences."

"It’s pretty crazy," said Gahn, who was in her sixth-grade keyboarding class when the planes hit the World Trade Center. "I don’t pretend to know a lot [about the subject], but the one thing you do know, the one name you do know, is Bin Laden."

Greg Hamot, the director of the UI Center for Human Rights, said he was left "speechless" by the news.

"It’s a huge symbolic event," said the professor of education. "It’ll vibrate throughout the world."

Tim Hagle, a UI political-science associate professor, said time will tell how the event will affect U.S.-Middle East relations.

"If we had gotten Osama bin Laden several years ago, within a couple years of 9/11, when it was sort of a more immediate kind of thing, it would have had a tremendous impact," he said.

But Hagle said the confirmation could still provide a morale boost for U.S. military operations in the Middle East and families of the victims of 9/11.

Harb Harb, the president of the Arab Students Association, said the event could spark a new chapter in American foreign policy.

"Right now, we’re in a situation where we can move forward from the tragedies in the past and work towards improving relations that can benefit both the U.S. and the Middle East," he said.

However, the U.S. State Department has put embassies on alert and cautioned Americans abroad of possible reprisal attacks, according to the Associated Press. The department said there is "an enhanced potential for anti-American violence."

"We will need to be more vigiliant, because there could be a lot of people who supported or admired bin Laden or Al Qaeda who will feel a heightened need to strike out at the U.S. if they can," said UI law Professor Adrien Wing.

Brian Lai, a UI associate professor of political science, said bin Laden’s real power in Al Qaeda began to wane some time ago.

"He mostly was just sort of an inspiration to them, but he had no real effect on any of their daily operations," Lai said.

Lai said the United States has been planning for bin Laden’s death for some time and was prepared to ramp up security in the event of his demise.

Al Qaeda was also blamed for the 1998 bombings of two U.S. embassies in Africa, killing 231 people and the 2000 attack on the USS Cole in Yemen, the Associated Press reported.

Former President George W. Bush congratulated Obama on Sunday night, according to the AP.

"The fight against terror goes on, but tonight America has sent an unmistakeable message: No matter how long it takes, justice will be done," Bush said in the statement.