The increase is "a clear demonstration that our alliance stands united in the face of any possible aggression," Stoltenberg told reporters at the NATO headquarters, a day ahead of a meeting of NATO defense ministers. "We have really shifted gears. The trend is up, and we intend to keep it up."
The increase — an estimate for 2017 — will boost military spending by non-U.S. NATO members to about $295 billion, which is still far less than the United States spends alone. Some of the spending increases were locked in before Trump's election in November.
NATO released only a portion of its updated numbers Wednesday, but its previous estimates for 2016 put the U.S. share of NATO defense spending at 72 percent.
The spending increases come after years of budget cuts up to 2014, as European nations trimmed spending on the belief that after the breakup of the Soviet Union, they no longer need to be ready to fight a war on their own soil.
But after the Russian seizure of Ukraine's Crimean Peninsula in 2014, NATO leaders pledged to increase annual defense spending to 2 percent of their gross domestic product by 2024. At a meeting in May, they said they would come up with concrete plans about how they would get there.
The spending increase announced Wednesday is $12 billion more than 2016 levels, and the increases are also growing bigger — 2016 spending was 3.3 percent higher than 2015 levels. Still, only five of NATO's 29 members meet the spending guidelines. Romania plans to get there this year, while Lithuania and Latvia expect to meet the bar in 2018.
Stoltenberg said that he was pleased that NATO nations were making progress.
"Many people thought that back in 2014 when we made that decision it was not obvious we were going to deliver," he said in a joint interview after his news conference.
Then-President Barack Obama also hit NATO allies for being overly reliant on the U.S. security umbrella, but Trump took the criticism to a new level on the campaign trail last year. Trump suggested that if a NATO member were attacked, he would first check their spending levels before he decided whether to come to their defense.
Then, at a meeting of NATO leaders last month that was designed for Trump to reassure his allies of U.S. defense commitments, he instead berated them for their spending and held back from an explicit commitment to Article 5 in the alliance's charter, NATO's bedrock principle that an attack on one country is the same as an attack on all.
Trump later made that pledge alongside the Romanian president in the Rose Garden, but the damage was done.
Stoltenberg said he was confident in U.S. pledges to NATO.
"For me, 'America First' is not America alone," he said in the interview, echoing a Trump mantra. "The best way to secure the United States is to be committed to NATO."
Defense Secretary Jim Mattis repeated the U.S. commitment Wednesday, speaking alongside his German counterpart, Defense Minister Ursula Von der Leyen.
"The U.S. commitment to our NATO Article 5 security guarantee is ironclad, as demonstrated over decades of our steadfastness and given voice more recently by President Trump before the American people," Mattis said in Garmisch, Germany.
Mattis said that the U.S. commitment to NATO deployments in Eastern European nations that feel threatened by Russia would last at least until 2020. He also pointed to a 42 percent increase in Trump's budget request for European military spending.
"Beyond any words in the newspapers, you can judge America by such actions," he said.
As they increase their spending, NATO allies have had to walk a fine political line, since Trump is deeply unpopular among their voters and any sign of capitulating to U.S. demands can now be toxic at the ballot box.
Allies have sought to cast their spending decisions as a response to their own need to defend themselves. Many of the 2017 spending decisions that together form the increase announced Wednesday were made before Trump's improbable November victory.
"I welcome the strong focus of President Trump on defense spending and burden sharing, because it is important that we deliver," Stoltenberg said Wednesday. "European allies should invest more in defense not only to please the United States, but they should invest more in defense because it is in their own interests."
Germany, Europe's richest nation, has been among the biggest laggards in the alliance, and its spending shortfall has been a major element in the Trump administration's deteriorating relationship with the country.
Von der Leyen, the German defense minister, said Wednesday that her country was working toward the spending goal.
"We need to have a fair burden sharing in Europe," von der Leyen said, speaking alongside Mattis in Germany. "If we want to have stability in the neighboring regions, we have to take responsibility for it."
Gibbons-Neff reported from Garmisch, Germany.