Federica Mogherini, High Representative of the European Union for Foreign Affairs and Security Policy | Lennart Preiss/Getty Images Mogherini pushes for two-speed Europe on defense France, Germany and Italy are keen to integrate EU security capabilities.

STRASBOURG — EU foreign policy chief Federica Mogherini wants member countries who are eager to integrate their defense capabilities to push ahead, without the need for treaty changes.

“We have the European framework to do it within the treaties," the EU's High Representative for Foreign Affairs and Security Policy said in an interview in Strasbourg earlier this week. "I know we have internalized that if some member states do something, it is not European. But it is European!”

France and Germany support a Mogherini proposal for some countries in the EU to combine their defense capabilities via a so-far unused provision in the Lisbon Treaty, called “permanent structured cooperation." This facility permits integration among a restricted group of nations, rather than requiring all member countries — 27, once Britain leaves — to sign up.

Participation in such a program would be “voluntary, inclusive and remains open,” according to a recent Franco-German document on security integration, which supports innovations such as a joint EU military headquarters, more cooperation with NATO, and a push for more cross-border military planning.

“Now is the time to deepen our cooperation, making the best possible use of the whole potential of EU treaties,” said the proposal by French Defense Minister Jean-Yves Le Drian and his German counterpart Ursula von der Leyen, which was prepared for Friday's informal EU summit in Bratislava.

Italy has gone even further, with Foreign Minister Paolo Gentiloni calling for a "Schengen of defense” in an opinion piece for POLITICO published this week.

Mogherini had already mentioned the possibility of using this tool in her Global Strategy document presented in June, and she is now preparing to follow up with an implementation plan. “Both in capital cities and in Brussels we have to understand that member states and EU institutions are the same, we are together, it's the EU," she told POLITICO.

"It applies also to the permanent structured cooperation: It's a possibility foreseen in the EU treaties, so it would be a group of member states going ahead within the European framework," said the 43-year-old former Italian foreign minister.

June's Brexit vote means there is no longer any need to take into account Britain's objections to defense integration in the EU. European Commission President Jean-Claude Juncker and European Council President Donald Tusk have now indicated this is a priority, and as well as the French, German and Italian backing, it has strong support in Central Europe, where the Czech and Hungarian leaders have called for the establishment of an EU army.

Mogherini believes there might still be a role for Britain in joint European military operations in future, even from outside the EU.

“For the moment we are 28. In the future, when they will not be a member anymore, they will not contribute to the definition of our priorities or actions, but there are many countries that are not part of the EU and take part into our missions and operations,” she said.

“We have experienced that there is an added value at doing things together as Europeans in the field of security and defense" — Federica Mogherini

Neither should the project be seen as competing with NATO, she said.

“We have clearly an awareness in the U.S. and in NATO and in Europe that developing an EU defense is not a way of competing, or taking away something from the transatlantic alliance, but it's a way of strengthening the transatlantic common work,” said Mogherini.

Once Britain leaves the EU, France and Italy will have the largest armed forces in the bloc. Some diplomats suggest that France is keen to promote an area of cooperation where it can surpass the Germans. France has demonstrated in Libya and Syria that it is ready to use its military force, and it has a permanent seat in the United Nations Security Council.

Mogherini believes there are grounds for optimism about military integration in Europe, pointing to the joint EU naval mission to fight people-smuggling in the Mediterranean, which was launched last year.

“We have experienced that there is an added value at doing things together as Europeans in the field of security and defense," she said. "This was not self evident 20 or 30 years ago. And Operation Sophia is the perfect example.”

“Whenever I present the plan to ambassadors, ministers...my last slide is that all of this requires political commitment,” she said. “At the moment I don't see resistance, at the moment I see readiness.”