Norwegian defence minister Ine Eriksen Søreide was photographed alongside Karin Enström (Sweden), Jeanine Hennis-Plasschaert (Netherlands) and Ursula von der Leyen (Germany) at the Munich Security Conference on Saturday.
According to the UK's Guardian newspaper, the idea for the photo came from Jeanine Hennis-Plasschaert, the Dutch defence minister, after the group met to celebrate the appointment of von der Leyen, the most recent of their number.
Hennis-Plasschaert tweeted out the photo alongside the words "onderonsje", meaning "huddle", after which it was picked up by the Guardian newspaper, among others.
"Neelie Kroes [a Dutch EU politician] once said to me that old boys' networks are the oldest form of cartels we have in Europe," Hennis-Plasschaert told the Guardian on Saturday. "She was right, but things are changing, and women can do similar things now."
According to the newspaper, when Pieter De Crem, Belgium's make defence minister, spotted the group, he joked: "Oh, I'll better get out of the picture."
Sweden's foreign minister, Carl Bildt, on Sunday tweeted out the photo along with the words "True Power Girls", sparking a Twitter flurry over whether he should have said "women".