Nine EU nations will formalise a plan to create a European military intervention force, with Britain backing the measure as a way to maintain strong defence ties with the bloc after Brexit.
The force, known as the European Intervention Initiative and championed by French President Emmanuel Macron, is intended to be able to deploy rapidly to deal with crises.
NATO Secretary General Jens Stoltenberg was attending the European Defence Ministers meeting in Luxembourg and said he did not see the initiative as a threat to the Alliance.
"I welcome this initiative because I believe it can strengthen the readiness of our forces because we need high readiness, that’s exactly what NATO is focussing on.
"So this comes on top of the fact we have already tripled the size of NATO's response force and we have established the VJTF [Very High Readiness Joint Task Force] so I just see new initiatives that complement and reinforce what is ongoing in NATO."
Britain has historically pushed back against deepening EU defence commitments, but with the UK due to leave in 2019 it will no longer be able to voice its concerns and the EU will find it easier to take these steps.
However, Prime Minister Theresa May has said the government will maintain its commitment to protecting Europe after Brexit.
The UK currently has the biggest defence budget of any EU member, making it an important asset to the EU.
Britain has a history of collaborative defence projects with EU countries including the Eurofighter Typhoon aircraft and the Meteor air-to-air missile.