Europe's economic powerhouse Germany and other NATO members have been reluctant to meet a commitment made in 2014 to spend two percent of GDP on defence by 2024.

"We are continuing the turnaround in defence spending, in 2019 alone we will spend four billion euros ($4.7 billion) more than we previously planned," Scholz told journalists in Berlin.

The increase will boost the military budget to 42.90 billion euros -- a "significant increase" and "clear sign" of Germany's commitment to its international obligations, he said.

But following years are set to see spending slow sharply.

The 2019 budget approved by Chancellor Angela Merkel's cabinet calls for defence outlays of 42.93 billion euros in 2020, 43.88 billion in 2021 and 43.86 billion in 2022.

The figures are well short of the 2.0 percent of GDP target.

Next year the ratio will hit 1.31 percent, before falling back to 1.23 percent by 2022.

NATO leaders are meeting in Brussels next week and Trump has written to Germany and seven other nations asking them to live up to their budget pledges.

Merkel acknowledged on Wednesday that her country must do more.

"Compared with what others are doing as a proportion of their GDP, it's far from enough. That's why we've committed ourselves to spending 1.5 percent of GDP by 2024," she told parliament.