Last week, the United States announced the withdrawal of some troops from the alliance's sensitive eastern European flank, on the front line against Russia during the invasion of Ukraine.

But the Pentagon simultaneously said Spain's contingent was playing "a fundamental and essential role for the defence of Europe and policies of deterrence", Spanish Defence Minister Margarita Robles said.

The Pentagon "congratulated Spain" for "contributing to the reinforcement of the Atlantic Alliance" and its more than 700 troops in Latvia, she added at a security forum in Madrid.

"Faced with those who want to say Spain is not a committed ally, Spain is a committed ally... and the Department of War recognised that last week," added Robles, referring to the US defence ministry by its new name.

The revelation contrasts with recent remarks by Trump, who threatened to expel and impose tariff "punishment" on Spain, which was NATO's lowest defence spender in relative terms last year.

In June, the 32-nation alliance agreed to massively boost defence spending to five percent of annual economic output over the next decade under pressure from Trump, who has raised doubts about the US commitment to European security.

But Spain insisted it would not need to hit the headline figure, saying it should meet its capacity objectives rather than fixed spending targets.