BRUSSELS -- The European Union unveiled plans Wednesday to promote defence co-operation and wiser military spending as U.S. President-elect Donald Trump warns NATO's European allies to start paying their fair share.

The European Commission said the multibillion-euro plan would fund research into areas like encrypted software or robotics and boost investment in joint projects across member states such as drones or helicopters.

It also aims to ease rules restricting defence procurement across borders, improve industry standards and adapt policies like the E.U.'s space program to security priorities.

"Our member states cannot afford to protect their citizens without deeper and better co-operation," European Commission Vice-President Jyrki Katainen told reporters.

The commission says E.U. countries have cut defence spending by nearly 12 per cent in real terms over the last decade but have failed to deepen military co-operation. It says this lack of co-operation is costing 25-100 billion euros ($27-106 billion) each year.

European defence spending is plagued by duplication -- around 80 per cent of defence procurement is done on a national basis -- a lack of interoperability between equipment owned by member nations and technological gaps. The failure to jointly produce defence programs also deprives the E.U. of important economies of scale.

The new plan could see security and defence research funding rise to about 90 million euros annually by 2020 and mobilize about 5 billion euros a year for joint projects.

Any national contribution to it could be taken into account when the E.U. assesses whether countries are respecting the bloc's budget deficit rules.

The plan is to be debated with industry and submitted to E.U. leaders for discussion at their summit on Dec. 15-16.

Twenty-two E.U. countries are also members of NATO. Only four of them spend NATO's agreed upon target of 2.0 per cent of gross domestic product on defence.

Trump suggested during campaigning that he might not defend allies that aren't pulling their weight. His campaign rhetoric rattled members of the E.U. and NATO worried about his relations with Russian President Vladimir Putin and an increasingly belligerent Moscow.