"We all agree that the European army is not something that is going to happen any time soon," Mogherini said after an informal meeting of the 28 European Union foreign ministers in Bratislava.
"But what can happen very soon, if member states are committed, is to advance in the field of European defence and that is what I put on the table today," she said.
However, a growing list of security challenges, from the migrant crisis to international terror, have emboldened the EU's executive arm, the European Commission, and Mogherini to push the idea forward.
"Fifty, 60, 100 years from now, who knows?," Mogherini told a briefing when asked about the possibility of a "European Army."
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"The important thing is that all the ministers appreciated the plans... Now is the time for real stuff and this is only the beginning," she added.
Mogherini said today that the foreign ministers were unanimous in backing the concept and she would now work on concrete proposals to put it into effect, suggesting the first operational results could be seen early next year.
British foreign minister Boris Johnson - who campaigned for Brexit - attended the meeting in Bratislava and said earlier that Britain remained committed to defence cooperation with the EU even though it had voted to leave the bloc.
Britain is an important, nuclear armed military power, plus it holds a veto as a permanent member of the UN Security Council.
EU leaders and top officials have recently stressed the possible role the bloc could play in ensuring security for its citizens in a dangerous world.
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