He called NATO obsolete. He said Germany’s acceptance of refugees is “utterly catastrophic.” The decades-old One China policy embraced by the United States? That’s up for discussion. Just days before Donald J. Trump’s inauguration, world leaders on three continents are on edge after comments the president-elect made in an interview on Friday with The Wall Street Journal and in a weekend interview with two European newspapers, Bild and The Times of London.

NATO is ‘obsolete’

“It’s obsolete, first because it was designed many, many years ago,” Mr. Trump said, according to the German newspaper Bild. The 28-member alliance, born in 1949, three years after Mr. Trump, is viewed by many — including his nominee for defense secretary, Gen. James N. Mattis — as essential to American security.

“Secondly, countries aren’t paying what they should” and NATO “didn’t deal with terrorism.”

Responding on Monday to Mr. Trump’s comments, Dalia Grybauskaite, the president of Lithuania, which gained its independence from the Soviet Union in 1991 and joined NATO in 2004, urged Mr. Trump to continue meeting the United States’ financial obligations toward the alliance.

“Since World War II, the presence of U.S. troops has been a prerequisite for rebuilding the Continent, safeguarding peace and ensuring security. We expect continuity from the new U.S. administration. Trump must maintain this leadership role, to ensure security, stability and peace.” — Ms. Grybauskaite

‘The force of Europeans is in their unity’

Mr. Trump also criticized the European Union, describing it as “basically a vehicle for Germany.” He praised Britain for its vote to leave the bloc, known as Brexit, adding: “I believe others will leave. I do think keeping it together is not going to be as easy as a lot of people think.”

“I think that we Europeans have our destiny in our own hands, and I would very strongly argue that we all stand together.” — Chancellor Angela Merkel of Germany, about the 27 European Union members that will remain after Britain’s departure

French leaders also bristled at Mr. Trump’s swipe against the bloc. Their response comes as they deal with growing domestic support for the anti-European Union and anti-immigrant party National Front, led by Marine Le Pen, who was spotted on Thursday at Trump Tower in New York.

“The best response,” said the French foreign minister, Jean-Marc Ayrault, “is European unity.”

“As with the case of Brexit, the best way to defend Europe is to remain united. This is a bit of an invitation that we are making to Mr. Trump. To remain a bloc. Not to forget that the force of Europeans is in their unity.” — Mr. Ayrault

China will ‘take off the gloves’

In the interview with The Journal, Mr. Trump said the One China policy was up for negotiation. Beijing responded quickly and decisively.