"This is essential for the continued strength of the transatlantic bond on which our alliance is founded," Stoltenberg said in NATO's 2016 annual report.
"For almost 70 years the unique partnership between Europe and North America has ensured peace and prosperity on both sides of the Atlantic," he said.
"That is an achievement we can never take for granted."
Trump caused dismay in Europe when he said on the campaign trail that NATO was "obsolete," and failing to meet the challenge posed by Islamic terror groups.
After the fall of the Soviet Union, NATO allies cut defence spending only to find themselves caught out by Russia's intervention in Ukraine and its 2014 annexation of Crimea.
NATO leaders, pressed by then US president Barack Obama, agreed the two per cent target in 2014 and reaffirmed it at a 2016 Warsaw summit to counter a more assertive Russia.
The NATO annual report said only five countries met the two percent target -- the United States, Britain, Greece, Poland and Estonia -- while Washington still accounted for nearly 70 per cent of combined alliance defence spending.
"In 2017, we must redouble our efforts to sustain the positive momentum and speed up national efforts to keep our pledge," Stoltenberg said in the report.
Meeting the two per cent target has caused some soul-searching in Europe over what the wider impact will be.
Critics cite the example of Germany, currently on 1.2 per cent of GDP but an increase to 2.0 per cent would put Berlin's defence budget on a par with Russia's at around 65 billion euros.
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