U.S. President Barack Obama urged a new international effort to understand and address the root causes of Muslim alienation, oppression and poverty, conditions that create fertile grounds for terrorist recruiters.

In a speech to the closing session of the three-day summit on combatting violent extremism, Mr. Obama said it was vital to change the distorted narratives used by Islamic State and al-Qaeda to lure disaffected and vulnerable youth.

"The notion that the West is at war with Islam is an ugly lie. And all of us, regardless of our faith, have a responsibility to reject it," he told senior officials and representatives from scores of countries – including Canada, represented by Public Safety Minister Steven Blaney.

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In his short intervention to the summit, Mr. Blaney admitted that his government was "caught by surprise by the terrorists' attacks" in Canada last October and that they prompted the new, far tougher measures to track, monitor and detain suspects as part of controversial legislation introduced this week in Ottawa.

Those measures will "further enhance the ability of Canadian government agencies to prevent and disrupt the evolving terrorist activity. … We must admit that we are facing a challenge within our borders," Mr. Blaney said, referring to the internal threat from radicalized individuals who can be expected to plot further attacks in Canada.

Although Mr. Obama spoke at the summit of an unwavering fight against terrorist organizations, he focused Thursday's speech on a call for a broader civil effort to create trust, inclusion and understanding.

"When people – especially young people – feel entirely trapped in impoverished communities, where there is no order and no path for advancement, where there are no educational opportunities, where there are no ways to support families, and no escape from injustice and the humiliations of corruption – that feeds instability and disorder, and makes those communities ripe for extremist recruitment," he said.

The President called for international action to confront economic grievances in these communities, especially by expanding education opportunities for girls.

To counter terrorist propaganda, "we need to do more to lift up voices of tolerance and peace," Mr. Obama said, promising new U.S. communications efforts to counter the luring narratives created by extremists. He urged other "nations to join in this work."

The President challenged "Muslim communities, including scholars and clerics" to "push back not just on twisted interpretations of Islam, but also on the lie that we are somehow engaged in a clash of civilizations."

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But Mr. Obama also said an international effort is required to address the genuine political grievances of millions of Muslims who live in oppressive regimes.

The President said groups such as al-Qaeda and Islamic State, which has carved out a nascent self-declared caliphate across a swath of Iraq and Syria, don't represent Islam, despite having attracted tens of thousands of jihadis, including many from Western nations.

Mr. Obama was under attack from critics at home and abroad for shying away from directly linking violent extremism to Islam.

That will doom his policy to failure, said Senator Ted Cruz, a Texas Republican and possible candidate for the 2016 presidential elections. "You cannot defeat an enemy if you refuse to acknowledge what it is," he said, adding: "The President and this administration dogmatically refuses to utter the words 'radical Islamic terrorism.'"

In a statement released by Mr. Blaney, the Canadian government didn't mince words. "Canadians are being targeted by jihadi terrorists simply because these terrorists hate our society and the values it represents."

That's the sort of blunt, uncompromising language that Mr. Cruz and other hawks want Mr. Obama to adopt.

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But others at the Washington summit echoed Mr. Obama's call to address root causes of alienation as well as attack extremist leaders.

"Military operations are crucial to confront real threats. But bullets are not the 'silver bullet,'" said United Nations Secretary General Ban Ki-moon. "Missiles may kill terrorists. But good governance kills terrorism."