Only eight of the 29 NATO member countries are forecast to reach this year the alliance's spending guideline of 2 percent of GDP as the world's biggest military alliance works to turn around over a quarter century of military cuts.
"To keep our nations safe, we need more defense spending, investment in key capabilities, and forces for NATO missions and operations," Stoltenberg told reporters at a meeting of NATO defense ministers in Brussels.
The ministers, including U.S. Defense Secretary Jim Mattis, were to announce the creation of two new command centers to cover trans-Atlantic maritime transport routes and logistics and transport within Europe.
The U.S. is expected to take responsibility for the Atlantic command, while Germany is best placed for the logistics hub. Allies are also likely to announce the launch of a new cyberoperations center.
NATO nations cut defense spending and slashed staffing at its commands after the Cold War, but Russia's annexation of Crimea in 2014, following its war with Georgia in 2008, has spurred the allies to boost military budgets.
U.S. President Donald Trump also publicly berated the Europeans and Canada at a summit last year, demanding that they start paying 2 percent on defense if they want Washington to stand by them in times of need. NATO leaders set that percentage as a guideline to aim for by 2024. Some, including Germany and Spain, will not make that benchmark.
The U.S. spends more on defense than all the other allies combined.
During the meeting Wednesday, Mattis told his allies to stump up more cash and military equipment, and provide more resources for NATO operations.
"You can't have either, or. It's got to be cash and capabilities and contributions," was the message Mattis delivered, according to a NATO official. The official briefed reporters on the condition of anonymity because he is not permitted to speak publicly about the closed-door deliberations.
The Europeans and Canada have boosted defense spending in each of the last three years, but British Defense Secretary Gavin Williamson said: "I've always seen 2 percent as a floor and not a ceiling, so just to hit 2 percent doesn't mean to say you're the world's best defense partner."
"We cannot expect to outsource our security obligations, Europe's security, to the United States," he said.
NATO allies are also expected on Thursday to launch planning for a mission to train military officers in Iraq and help build up the conflict-torn country's military academies.
Lolita C. Baldor in Brussels contributed to this report.
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