The decision marks the first time the bloc has opened up an initiative from its Permanent Structured Cooperation (PESCO) pact to involvement from outside nations.

German Defence Minister Annegret Kramp-Karrenbauer hailed the move as a "quantum leap in concrete cooperation when it comes to ensuring that troops can be deployed in Europe across national borders".

"This is a very important topic, not only for the European Union, but also for NATO," she said.

The push to facilitate troop transfers around the continent has gathered steam in the face of increased anxiety over Russian aggression since Moscow's annexation of Crimea from Ukraine in 2014.

EU foreign policy chief Josep Borrell said the joint project would make the bloc's "defence more efficient and contribute to strengthen our security".

The EU has designated 1.7 billion euros ($2 billion) over the next seven years to helping bolster "military mobility" including by upgrading infrastructure like bridges, rail and roads.

The Dutch-led project aims to cut bureaucratic waiting times for the cross-border movement of troops.

"The admission of these three key EU partners and NATO allies to the EU project is of great significance to the transatlantic bond and will further contribute to enhance EU-NATO cooperation in this area," the Dutch defence ministry said.

All but two EU nations signed up to the landmark PESCO agreement in 2017 to increase cooperation as the bloc's ambitions on common defence gained pace.

- NATO welcomes move -

NATO Secretary General Jens Stoltenberg -- who was meeting the EU defence ministers at their first in-person gathering in a year -- welcomed the move.

"Non-EU allies play an essential role in protecting and defending Europe," he said.

He pointed to major NATO military exercises about to start that will see US, Turkish and British troops deployed on the continent.

"It demonstrates also the importance of moving NATO troops quickly through Europe and that's also a reason why military mobility is so important."

Debate has raged for decades over what role Brussels should play on defence, and EU member nations, most of which are also NATO allies, have often been reluctant to integrate military capabilities.

The departure of Britain from the bloc saw the EU lose significant military and diplomatic heft, but it also removed from the Brussels conversation a fierce opponent of anything that might lead to a European army.