The head of NATO was forced to offer public assurances that the alliance remains firmly committed to its mission after Donald Trump expressed hesitance on Wednesday that the United States would honor NATO’s security guarantees to its member countries.

“Solidarity among allies is a key value for NATO. This is good for European security and good for US security. We defend one another,” NATO Secretary General‎ Jens Stoltenberg told BuzzFeed News in an interview published on Thursday.

“Two world wars have shown that peace in Europe is also important for the security of the United States,” he added.

Stoltenberg’s comments come after Trump gave a troubling interview to the New York Times on Wednesday, suggesting that he was not willing to help all NATO nations in need.

When asked if he would assist the Baltic states that have recently joined NATO in combatting Russian aggression, Trump said he would help only after assessing whether those countries “have fulfilled their obligations to us.”

Trump’s comments could embolden Putin’s Russia, cause distress among America’s European allies, and undermine the careful decades-long work of forging a lasting European peace. They come after the Trump campaign worked to soften language in the 2016 Republican platform about helping Ukraine fight Russian forces. The platform will not call for the U.S. to supply arms to Ukraine, despite broad support among Republicans for helping Ukraine fight Russian forces if necessary.