After years of cutting defense spending, America's NATO allies are on track this year to spend more — an overall increase estimated at about $3 billion, according to NATO's secretary-general.

Twenty of the 27 U.S. allies in NATO plan to spend more on defense in real terms this year, alliance chief Jens Stoltenberg said Monday.

"After many years of going in the wrong direction, we are starting to go in the right direction," Stoltenberg told reporters. "But we are still far from where we need to be."

NATO leaders in 2014 committed to spending 2 percent of the countries' national income on defense to meet new security challenges ranging from Russia to Islamic extremism. But only the U.S., Britain, Estonia, Greece and Poland currently spend that much or more.