The Obama administration says it will take more than air strikes in Syria or friendly troops in Iraq to defeat the militant group that calls itself the Islamic State, which is also known as ISIS or ISIL. The White House says it will also take community outreach in places like Boston and Minneapolis.

Preventing homegrown terrorism is the focus of meetings at the White House this week. President Obama will address the White House Summit on Countering Violent Extremism Wednesday afternoon.

Counter-terrorism experts say more than 20,000 foreign fighters have traveled to Syria to sign up with ISIS, including at least 3,400 from western Europe and the United States.

Attorney General Eric Holder says it's those western radicals who keep him awake at night. He worries about the threat they could pose if they bring their extremist ideology home from the battlefield. Or if — like the suspected gunman in Copenhagen — they never leave home at all.

"The ultimate solution to this is to make sure that the young men who might be attracted to that siren song have to be dealt with," Holder says. "They have to be made to feel a part of our communities. I think we do a better job perhaps than other nations of integrating those people who might be attracted to the ISIL call. But we have to re-double our efforts."

Participants in the summit will hear about pilot programs in Boston, Los Angeles and Minneapolis, where local officials have tried to combat radicalization. Those efforts have included law enforcement, but also the business community, teachers, families, churches and mosques.

Muslim leaders have cautioned that outreach efforts could backfire, if they're perceived as a tool for intelligence gathering or if Muslim communities are singled out for attention.

The White House has taken pains to say it's worried about all forms of violent extremism. Obama argues that religious tolerance is one of the United States' most powerful weapons.

"One of the best antidotes to the hateful ideologies that try to recruit and radicalize people to violent extremism is our own example as diverse and tolerant societies that welcome the contributions of all people, including people of all faiths," Obama says.

The summit continues Thursday with a gathering of international leaders at the State Department.

Copyright 2021 NPR. To see more, visit https://www.npr.org.