US President Barack Obama says the US is "not at war with Islam - we are at war with the people who have perverted Islam".
He was speaking to representatives from 60 nations attending a three-day event on extremism that follows attacks in Denmark and France.
Mr Obama said the world had to confront the ideologies that radicalise people.
He said those heading groups like Islamic State and al-Qaeda were not religious leaders but terrorists.
Mr Obama said associating Islamic State or al-Qaeda with Islam would be buying into the propaganda of those groups, challenging critics who have questioned him for not describing recent attacks as the work of "Islamic radicals".
Mr Obama has asked Congress formally to authorise military force against Islamic State in Iraq and Syria. The US and its partners have carried out air strikes against the group since last year.
Analysis: BBC's Barbara Plett Usher in Washington
The idea for the conference came from Islamist-inspired attacks in Canada and Australia, and it was announced right after the Charlie Hebdo shootings in France.
Given that context, the White House has been criticised for resolutely refusing to link violent extremism with the religion of Islam. But President Obama has forcefully held his ground, arguing that denying religious legitimacy to terrorists is an important part of countering the radicalisation of potential recruits.
Prevention is the focus of the conference. It's mobilised people from the trenches in the battle for hearts and minds to share best practices: everyone from teachers to entrepreneurs to Silicon Valley executives have been talking about community outreach to marginalised youth and counter-messaging Islamists on social media.
International delegates will also have their say. But critics say the topic may be too broad to result in any meaningful action from a conference with more than 60 nations represented. Administration officials talk about an action plan, but they've described it vaguely as a "catalyst activity" rather than a concrete outcome.
Ripe for radicalisation
Mr Obama said the fight against violent extremism could not be won by military power alone.
Communities, he said, must do their part. "These terrorists are a threat first and foremost to the communities they target," he said.
He added that there were Muslims around the world who did not necessarily subscribe to the violent tactics of IS, but who "buy into" the notion that Islam had been "polluted" by Western values.
"It makes individuals… more ripe for radicalisation," he said.
"Muslim leaders need to do more to discredit the notion that our nations are determined to suppress Islam."
UK Home Secretary Theresa May and Paris Mayor Anne Hidalgo are among those attending the conference in Washington.
The US and its allies are also concerned about growing extremist involvement in Libya and West Africa, as well as Americans and Europeans who have joined IS.
The summit comes at a time of heightened tension on both sides of the Atlantic. Canada has faced a growing threat from Islamist radicals, with two soldiers dying in separate "lone wolf" attacks in October last year.
Meanwhile Europe has been on heightened alert since the Charlie Hebdo shootings in Paris in January. Those attacks were followed by last weekend's killings in Copenhagen.
Worry and fear
Mr Obama also wrote an editorial published by the Los Angeles Times. In the piece he said groups like al-Qaeda and [IS] "exploit the anger that festers when people feel that injustice and corruption leave them with no chance of improving their lives".
"The world has to offer today's youth something better," he wrote, adding "governments that deny human rights play into the hands of extremists".
And in both his speech and the editorial, Mr Obama referenced the recent murders of three Muslim students in North Carolina.
"We do not yet know why three young people, who were Muslim Americans, were brutally killed in Chapel Hill, NC."
"But we know that many Muslim Americans across our country are worried and afraid."
(Published by BBC News - February 19, 2015)