Member states approved plans in March for a small grouping in Brussels to coordinate three of the bloc's overseas training operations.
After months of tough negotiations, all 28 member states approved plans in March for a small grouping in Brussels to coordinate three of the bloc's overseas training operations.
Turning the agreement into a legal text however has run into trouble, with proposals to call it an "Operational Headquarters" being a "red flag" for Britain ahead of its June 8 election and the start of the Brexit talks, the diplomatic sources said.
"We are still trying to find a compromise with our British friends on the legal position so that this structure can be set up," said one of sources who asked not to be named.
"They are extremely sensitive to the elections and how it might be seen back in the UK," the source added.
British officials in Brussels declined to comment.
EU foreign ministers meet Monday in Brussels to review progress on the March accord, with defence ministers due to approve their findings on Thursday.
EU foreign affairs chief Federica Mogherini, who chairs Monday's meeting, has pushed hard for the EU to take on an increased military role after President Donald Trump cast doubt on the US security commitment to Europe.
Britain's departure will deprive the bloc of both a nuclear-armed power which wields a UN Security Council veto and a member state which has consistently opposed EU defence integration as a risk to NATO.
Mogherini, top officials and member states led by France and Germany believe that against this backdrop, the European Union must now do much more on defence.
The March agreement set up what is known as the Military Planning Conduct and Capability (MPCC) facility to oversee the EU's "non-executive military missions".
These are currently civil-military training operations in Mali, the Central African Republic and Somalia which do not involve the use of force.
The EU has also mounted Operation Sophia in the central Mediterranean, which can use force to stop migrant smugglers, and the Operation Atalanta anti-piracy mission off the Horn of Africa.
These two executive operations have their own command centres which will remain separate from the MPCC.