A statement by US President-elect Donald Trump that Nato is "obsolete" has caused "worry" in the alliance, Germany's foreign minister says.
Frank-Walter Steinmeier said it was a contradiction of comments made days ago by Mr Trump's incoming defence chief.
Mr Trump also said German Chancellor Angela Merkel had made "a catastrophic mistake" by admitting more than one million migrants.
And he threatened German car makers with high import tariffs.
Shares in BMW, Volkswagen and Daimler fell after he warned that cars built in Mexico, where they have invested in factories, would be taxed at 35% if exported to the US.
BMW said the company would stick to its plans to open a Mexican plant in 2019.
Mr Trump was giving an interview in New York to two British and German newspapers, the Times and Bild, at Trump Tower.
Nato, Mr Trump said, had been forged "many, many years ago" and had become "obsolete because it wasn't taking care of terror".
Mr Trump reiterated his criticism that "a lot of" Nato's 28 member states were not paying their fair share.
"A lot of these countries aren't paying what they're supposed to be paying, which I think is very unfair to the United States."
Figures released by Nato show that just five member-states met or surpassed its defence spending goal - 2% of GDP - last year.
Mr Trump added that Nato was "very important" to him.
Speaking in Brussels after consulting Nato Secretary-General Jens Stoltenberg, Mr Steinmeier said the president-elect's comments had caused "worry and concern".
"This is in contradiction with what the American defence minister said in his hearing in Washington only some days ago and we have to see what will be the consequences for American policy," the German foreign minister said.
Only last week, the US deployed 3,000 soldiers, 80 tanks and hundreds of armoured vehicles to Poland in a move by President Barack Obama to reassure Nato allies concerned about a more aggressive Russia.