Obama Vows to Stand With Allies Against Terror 'Scourge'

President Obama today vowed that the U.S. will stand with its allies to combat the "scourge" of terrorism.

Extremism "is a problem that causes great heartache and tragedy and destruction, but it is one that we're ultimately going to defeat," he said from the East Room of the White House.

"We will continue to do everything in our power to help France seek the justice that is needed," Obama said of the terror attacks in Paris that killed 17 people last week.

Since the Paris raid, Europe has been on edge, with authorities rushing to identify individuals with links to ISIS and al Qaeda.

Police in Belgium on Thursday killed two members of a terror cell who reportedly plotted to gun down police, and French and German authorities have arrested more than a dozen people allegedly tied to Islamic extremists in the past few days.

However, the president said, the United States has "one big advantage" over some European countries when it comes to avoiding homegrown terror attacks: "Our Muslim populations, they feel themselves to be Americans."

"Now, it doesn't mean that we aren't subject to the kinds of tragedies that we saw at the Boston Marathon," he acknowledged, "but that, I think, has been helpful. There are parts of Europe in which that's not the case."

Obama emphasized the need to combat the threat not just militarily, but also by "inoculating" citizens against extremist ideologies, lifting up mainstream Islam "as aggressively and as nimbly as the messages coming out from these fanatics."

Obama spoke alongside visiting British Prime Minister David Cameron during a joint press conference following a meeting in the Oval Office.

"The world is sickened by terrorism," Cameron told reporters. "We know what we're up against, and we know how we will win."

At a dinner Thursday evening at the White House residence, Cameron reportedly pressed Obama for greater government cooperation with online and social media companies to allow surveillance of potential terrorists.

The administration has sought to balance the need for intelligence with privacy concerns.

"I'm confident we can balance these imperatives," Obama said at the press conference. "We shouldn't feel that just because we've seen such a horrific attack in Paris, that everything should be going by the wayside."

"We've got to make sure that we don't overreact, but remain vigilant," he added, noting that the administration is working with social companies to solve "technical issues."

ABC News' Devin Dwyer contributed to this report.