The success of a key NATO summit next week is hanging in the balance. Spain has announced that it cannot raise the billions of dollars needed to meet a new defense investment pledge.

Spain has asked to opt out of NATO's plan to increase members' defence spending to 5% of their gross domestic product, a move that could derail a summit at which the military alliance plans to ask them to commit to the target.

"Committing to a 5% target would not only be unreasonable, but also counterproductive, as it would move Spain further away from optimal spending and would hinder the EU's ongoing