According to information available to Politico, the defense ministers of France, the UK, Germany, Italy, Spain, the Netherlands, Belgium, Portugal, Denmark, and Estonia will sign a letter of intent in Paris in June, "pledging to develop a common strategic culture, share analysis and foresight on trouble spots that may require intervention and work to coordinate their forces for future operations".

"Frustrated by the big-tent, low-ambition start to the European Union's so-called Permanent Structured Cooperation (PESCO) in defense agreed last year  at Germany's insistence, the French leader is pressing ahead with a small core of like-minded nations outside EU and NATO institutional structures," Politico wrote, adding that the coalition would also provide an opportunity for the UK to be tied into European defense cooperation after leaving the EU.

"By involving Estonia, they made sure they have an Eastern EU member country on the frontline with Russia engaged from the outset," Politico said.

Macron outlined the idea in a speech on European integration at the Sorbonne last September, where he called for a common European intervention force, defense budget, and doctrine for action in contingencies where the United States and NATO may not get involved.

France wants to recruit allies that could help share its military burden especially in Africa, where it intervened alone in Mali in 2012 to prevent Islamist militants from seizing control of a weak state.