Italy's Prime Minister Giuseppe Conte (L) shakes hands with the President of the United States Donald Trump on the first day of the G7 Summit.

There could be fresh tensions over NATO contributions with Italy's defense minister suggesting the rules should be changed on how countries contribute to the military alliance.

Members are obliged to spend the equivalent of 2 percent of their own gross domestic product (GDP) on national defense. These payments are used "to meet the needs of its armed forces, those of allies or of the alliance," to pay pensions to retired military, to contribute to NATO-managed trust funds as well as research and development.

However, Elisabetta Trenta, the defense minister of the southern European nation, said in an interview that this rule should be broadened out.

"There are parts of our spending that are related to defense but are not in the defense budget," she told the Financial Times in an interview published Monday, suggesting that areas such as cybersecurity should feature in the target. A spokesperson for Italy's defense ministry was not immediately available for comment when contacted by CNBC. A NATO spokesperson did not want to comment on the interview.

Contributions to NATO are a highly sensitive topic. President Donald Trump has often criticized other NATO members for not respecting the spending rule. Speaking at a NATO summit in 2017, Trump said: "Over the last eight years, the United States spent more on defense than all NATO countries combined. If all NATO members had spent just 2 percent of GDP on defense last year, we would have had another $119 billion for our collective defense."