The secretary general of NATO has supported demands from the U.S. for European and Canadian members to increase their contribution towards the North Atlantic defense alliance.
Jens Stoltenberg told CNBC Saturday that the demands from the new Trump administration were "firm and fair" and come at a time when NATO is needed more than ever.
President Donald Trump has heavily criticized the NATO defense alliance and has signalled plans to withdraw unless European countries increase their defense spending to at least 2 percent of their gross domestic product, an agreement initially laid out by the 28 member states in 2014.
On Wednesday, U.S. defense secretary James Mattis reiterated that the U.S. would "moderate" support if these demands were not met.
"The message from secretary Mattis was very firm and fair because it is fair of the U.S. to ask for more defense spending across Europe and Canada," Stoltenberg told CNBC.
Stoltenberg said Europe and Canada were "moving in the right direction", with the alliance seeing a 4 percent increase in real spending in 2016.
Meeting the target will take longer for some countries than others, he admitted, and said he was confident all allies will meet the benchmark within a decade, as promised.
The contentious spending debate comes at a crucial time for NATO, as the partnership faces increased threats from conventional sources as well as cyber-terrorism and a "more assertive Russia", Stoltenberg said.
"We are seeing a more assertive Russia. We are seeing a Russia which has invested heavily in new military capabilities, which has tripled its spending on defense over the last years and, most important, which has been willing to use military force against neighbors in Georgia and Ukraine."
Stoltenberg said NATO is responding by increasing its presence in the East with new battle grounds and a bigger military presence.
"We have to be agile, we have to be prepared for the unforeseen, and that's exactly what we are doing."