Germany was "determined to come as close to the two-percent target as possible with the options we have and to reach the two-percent target in this legislative period", ending in 2025, Chancellor Olaf Scholz's spokesman Steffen Hebestreit told a regular press conference.

Days after the Russian invasion of Ukraine, Scholz announced a 100-billion-euro ($106-billion) fund to beef up Germany's military defences and offset decades of chronic underfunding.

But the spending programme has struggled to get off the ground, as industry strains to keep up with demand and key purchase plans are held up.

"A balanced and resilient transatlantic partnership also requires that Germany and Europe play active roles," Scholz wrote in an article for Foreign Policy magazine published on Monday.

Germany would increase its investments to hit NATO's spending target and develop an army "that we and our allies can rely on", Scholz said.

However, the goal could not be reached "overnight", Hebestreit said.

There were "European regulations to observe", as well as procurement challenges that needed to be overcome, he said.

"We are in a market where there is a lot of demand, which significantly exceeds supply," leading to delays in delivery, he said.

Internal wrangling over how the money should be spent has also bogged down spending decisions.

The planned purchase of 35 US-made F-35 fighter jets was thrown into doubt on Sunday, as it emerged defence ministry officials had raised serious concerns.

The ministry pointed to potential "delays and additional costs" in the nearly 10-billion-euro project, according to a document seen by AFP.