NATO military chiefs have been meeting this week to prepare a crucial summit next month in Brussels that will decide the alliance's budget.
But it comes at a time when the EU is looking at expanding its military cooperation, sparking questions of whether the two overlap.
Brussels has given its European Defence Fund -- which aims to increase cooperation between states and hike defence research spending -- a budget of €7.95 billion for the 2021-2027 period. EU military representatives also met this week.
Italian military chief Roberto Nordio attended both meetings. He told Euronews that "cooperation between the NATO and the EU is not easy".
"Why should a European citizen spend twice: for the EU and for the NATO?" asked Lieutenant General Nordio, before adding that cooperation "is already operational and it's bound (...) to grow along a difficult path".
Spending has been a key issue for NATO in recent years. In 2006, allies agreed to spend 2% of their GDP on defence, but so far only 11 of the 30 members are doing so. The US, the biggest spender, has demanded -- especially under the administration of Donald Trump -- that all members live up to this commitment.
Watch the interview with Nordio in the video player, above.