By Inti Landauro, Aislinn Laing and David Latona

MADRID (Reuters) -Spain has asked NATO to opt out of increasing its defence spending to 5% of GDP, a move that could derail a summit at which the military alliance will ask members to commit to the spending target.

In a letter sent to NATO chief Mark Rutte and seen by Reuters on Thursday, Prime Minister Pedro Sanchez requested a "more flexible formula" that either makes the spending target optional or excludes Spain from its application. 

He said it was not Spain's intention to obstruct the outcome of next week's NATO summit. But any agreement to raise defence spending, in response to a request by U.S. President Donald Trump, would require unanimous approval by the 32 member states.

"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 efforts to strengthen its security and defence ecosystem," Sanchez wrote in the letter.

"It is the legitimate right of every government to decide whether or not they are willing to make those sacrifices. As a sovereign Ally, we choose not to," he added.

Rutte has proposed that member states agree to boost defence spending to 3.5% of gross domestic product and commit a further 1.5% to broader security-related spending to meet Trump’s demand for a 5% target. 

Asked for comment about Spain's request, a North Atlantic Treaty Organization official said: "Discussions among Allies on a new defence investment plan are ongoing."

NATO’s current defence spending goal is at least 2% of GDP. Leaders across NATO say that goal is no longer sufficient, as they see Russia as a bigger threat since its 2022 invasion of Ukraine.

SPAIN'S CONCERNS

Sanchez said that rushing to a 5% target would harm European Union efforts to become self-reliant in defence production, pushing member states to procure equipment outside the bloc.

Trump has said NATO members are not spending their fair share on defence and has threatened not to come to the aid of fellow NATO members that do not spend enough. 

The U.S., which has been Kyiv's primary military backer since Russia's invasion, spent an estimated 3.38% of GDP on defence in 2024, the third most among NATO nations, according to NATO.

The new target proposed by the U.S. was "incompatible with our welfare state and our world vision," Sanchez said.

Instead, Madrid considers it will need to spend 2.1% of GDP to meet the Spanish military's estimated investment requirements, Sanchez said.

Some other NATO members have questioned the timeline, saying it is too rapid, but are generally willing to sign up, diplomatic sources say.

Italy wants the deadline moved to 2035 from 2032 and wants to eliminate a requirement to increase spending by 0.2% per year, giving more freedom on annual increases as long as the final target is met, a source with knowledge of the matter said.

(Reporting by Inti Landauro, Aislinn Laing and David Latona; Writing by Charlie Devereux; Editing by Timothy Heritage)