United States, European Leaders 'Finalizing' Russian Sanctions

NATO leaders are reportedly organizing a rapid-response force.

Obama Takes on ISIS Threat at NATO Summit

Eastern Hopes for NATO Bases Stymied by Russia

"We must be able to act more swiftly," Cameron said. "I hope that today we can agree a multinational spearhead force deployable anywhere in the world in just two to five days."

During the summit, Cameron and President Obama have been seeking support from their counterparts for a campaign to degrade Islamic State militants that have wreaked havoc in Iraq and Syria.

Obama is scheduled to speak at a news conference at 11:30 a.m. ET today after a ceremonial NATO flyover event and meeting with world leaders. He is expected to return to the White House this evening.