Donald Trump is "predictable" and his return to the White House will bring clarity to US-Europe ties, conservative leader Friedrich Merz, the favorite to become Germany's next chancellor, said on Saturday.

"Trump is very predictable. He means what he says and he does what he says," the CDU head told a press conference in Berlin. 

"That means there will be much more clarity," he said.

Trump wants NATO member states to increase defense spending to five percent of GDP, at a time when Germany has only just reached the two percent mark for the first time. 

"Trump is now speeding up a process in Europe that we should have undertaken," said Merz of the debate over financial contributions to the transatlantic military alliance. 

Merz is frontrunner in opinion polls to replace outgoing chancellor Olaf Scholz in a snap general election on 23 February. 

Defense Minister Boris Pistorius said earlier on Saturday Germany should aim to spend around three percent of national output on defense. 

Merz, who advocates greater integration between European Union states, said he hoped Trump's inauguration on Monday would "speed up our efforts to bring our power together and act together". 

He said Europe had nothing to "fear" from a new Trump presidency. 

"Europe has more inhabitants than the United States and Canada combined. If we are united... we can achieve things," he said, alluding in particular to defense.

Trump said during his election campaign he could end the conflict between Russia and Ukraine in fewer than 24 hours. 

His entourage has since indicated he needs more time but talks could nevertheless start soon at a meeting between Trump and Russian President Vladimir Putin.

"The most important thing is that we achieve peace in Ukraine as quickly as possible. But this peace must not be reached behind Ukraine's back" nor the backs of the Europeans, Merz said.