But neighbouring Spain, bottom of the pile of NATO members' defence spending as a proportion of output, refused to budge on its timeline of hitting the two-percent mark by 2029 during a visit by alliance chief Mark Rutte.

Portugal's announcement came after the return to power of US President Donald Trump, who has frequently castigated European members of the alliance for not investing enough in their militaries.

The mercurial Republican has in the past thrown into question whether the United States would protect NATO members who did not meet the spending threshold, which he recently suggested should be raised to five percent of GDP.

At just 1.55 percent of its 2024 GDP, Portugal's investment in defence places it close to the bottom of the list.

Lisbon committed at last summer's NATO summit in Washington to reach the two-percent threshold by 2029.

And after a meeting on Monday with Rutte in Lisbon, Portuguese Prime Minister Luis Montenegro said his country was "ready to bring forward even further the timetable for our trajectory of investment in this area".

- 'Security beyond spending' -

Montenegro said that decision was made with "current geopolitical circumstances" in mind.

However, he denied that Trump's return to the White House had influenced the choice to accelerate Portugal's spending plans.

Rutte said he welcomed the increases in the country's defence spending.

"But we also know that the goal of two percent, now set a decade ago, will not be enough to meet the challenges of tomorrow," the former Dutch prime minister added.

Rutte then travelled to Madrid for talks with Spanish Prime Minister Pedro Sanchez, whose country spent just 1.28 percent of its national output on defence in 2024.

The Socialist leader told Rutte "Spain is a serious, responsible and committed ally within NATO" and "underlined the firm commitment" to reach two percent by 2029, Sanchez's office said.

Spain has boosted its defence investment by 70 percent in the past decade and Sanchez "highlighted that security goes far beyond defence spending", his office added, citing the country's participation in "all of NATO's main missions".