EU foreign affairs chief Federica Mogherini is thought to be preparing to put forward a timetable setting out steps to create EU military structures "to act autonomously" from the western alliance.
The Italian official has reportedly told diplomats from the European External Action Service that the military plan - branded by some countries as the foundation of a "European army" - represented a chance to relaunch itself after the "shocking result" of the referendum on EU membership.
"We have the political space today to do things that were not really doable in previous years," Mogherini told EU ambassadors.
The military plan foresees countries such as France, Germany, Italy, Spain and Poland creating permanent military structures to act on behalf of the EU and for the deployment of the EU's battle groups and 18 national battalions.
It could also comprise an EU military planning and operations headquarters in Brussels that could be a rival to Nato. Last week, the Czech Republic and Hungary backed the plan as the basis to "setting up a joint European army."
A timetable for the plan will be discussed at a meeting of 27 EU leaders - excluding Theresa May - at a summit in Bratislava on 16 September.
A succession of UK governments have previously opposed the creation of a fully-fledged European army, but the European Commission, France, Germany and Italy see Brexit as a new chance to press ahead with deeper EU military integration.
Nato officials have expressed concerns that the proposals will create rivalry and challenge the alliance's primacy as the main defence structure.
Tory MEP Geoffrey Van Orden, his party's defence spokesperson, commented, "In all the debate on Brexit, there is a worrying lack of focus on the implications of the EU's defence ambitions. We can all see that the EU might play a useful role in conflict prevention and in some civil aspects of crisis management."
Van Orden added, "But its ambitions go beyond that. The EU motive is not to create additional military capability but to achieve defence integration as a key step on the road to a federal EU state.
"The US and indeed the UK are being misled if they imagine that such moves will enhance Nato - the key guarantor of our collective defence.
"On the contrary, creation of EU defence structures, separate from Nato, will only lead to division between transatlantic partners at a time when solidarity is needed in the face of many difficult and dangerous threats to the democracies."
Ukip MEP Mike Hookem, his party's defence spokesperson, said, "This is something Ukip has been warning about for years and I'm pleased to see people are finally waking up."
He added, "An EU army is not some Eurosceptic fantasy, there are many in Brussels hell-bent on making it happen."
Pauline Massart, a defence expert with the Friends of Europe think tank, said, "With the UK voting to leave the EU, France is the only member state left with both proper operational capability and the political will to use it, an unsustainable position in the long-term.
"It's interesting to see that largely Eurosceptic leaders in Eastern Europe have quickly rallied to the idea of strengthened European defence cooperation.
"But few of the countries which have so far expressed interest in the project cite the same reason, which range from budgets and migration to a resurgent Russia or independence from NATO.
"Any increased cooperation in European defence would certainly have strong symbolic value at a time of profound doubt in the European project."