Former foreign ministers and secretaries of state, including New Zealand's Sir Don McKinnon have written to US President Donald Trump warning him about his "deteriorating relationship" with his allies.
The letter was sent to Mr Trump before he left for a trip to Europe where he's expected to have tense talks with the leaders of NATO member nations.
Mr Trump has accused NATO countries of underfunding the security alliance and unfair trade with the US.
The letter from 16 former foreign ministers, including former US Secretary of State Madeleine Albright says "we are gravely concerned about the deteriorating relationship between the United States and its Western allies".
It urges Mr Trump to "reverse this dangerous trend."
The letter says threats to security and prosperity are multiplying.
"We believe that the best answer to these challenges is a cooperative and productive partnership between the United States, Canada and Europe.
"This week, you can move beyond recent signs of acrimony and reaffirm the health and common purpose of the Atlantic alliance. We urge you to seize this opportunity."
Ms Albright, who was secretary of state during the Clinton administration, told the Politico news site that the mood in Europe was one of "both fear and confusion".
"It's been a very, very long time that I have seen such concern about what is going on and trying to read where the United States is", she was quoted as saying.