Spain's prime minister defiantly declared "No to war" on Wednesday, deepening a rift with the United States after Madrid refused to use its bases to attack Iran and Washington threatened trade retaliation.

Spain's socialist prime minister, Pedro Sanchez, had already angered US President Donald Trump with a series of other policies.

Sanchez has refused to join NATO allies in a pledge to increase defense spending to five percent of GDP, as Trump demanded, and has sharply criticized Israel's war in Gaza.

Trump attacked Sanchez's government on Tuesday, calling Spain a "terrible" ally and threatening to cut off all trade with Spain.

Sanchez defended his stance on Wednesday, saying his government's stance "can be summed up in four words: no to war."

"We will not be complicit in something that is harmful to the world and contrary to our values ​​and interests, simply out of fear of retaliation," he added in a televised speech.

Spain is part of the European Union, which allows goods to move freely between its 27 countries. This would complicate any attempt to impose trade restrictions on a single member state.

"Trump's words don't always become policy. We'll have to see if and how he implements them," said Angel Saz Carranza, director of the Esade Center for Global Economics and Geopolitics, a Spanish think tank.

The President of the European Council, Antonio Costa, wrote on X that he had called Sanchez to "express the EU's full solidarity with Spain."

"The EU will always ensure that the interests of its member states are fully protected," Costa said.

French President Emmanuel Macron also called to "express France's European solidarity in response to the latest threats of economic austerity aimed at Spain," his office said.

US forces use the Rota naval base and Moron air base in southern Spain under an agreement signed in 1953 under the dictatorship of General Francisco Franco.

During the 2003 invasion of Iraq, Spain, then led by conservative Prime Minister Jose Maria Aznar, strongly supported the United States by sending troops.

Spain's participation in the Iraq war sparked large street demonstrations, and many Spaniards blamed it for the train bombings in Madrid on March 11, 2004, which killed nearly 200 people.

An al-Qaeda affiliate claimed responsibility for the attacks and called for the withdrawal of Spanish forces from Iraq.

Sanchez on Wednesday compared Iran's attacks to the Iraq war, which he said increased terrorism, raised energy prices and led to a less secure world.

"We oppose this catastrophe," he said, referring to the Iran war.

In contrast, neighboring Portugal authorized the United States to "conditionally" use an air base in the Azores archipelago in the Atlantic Ocean for attacks on Iran, Prime Minister Luis Montenegro told parliament on Wednesday.

The authorization was granted as long as “these operations are defensive or retaliatory, are necessary and proportionate and are aimed exclusively at military objectives,” Montenegro said.

The conservative leader said these conditions were "in line with international law", but he refused to openly support Sanchez or take a stance on US-Israeli attacks on Iran.

The Spanish prime minister has emerged as a prominent figure for Europe's disillusioned progressives, who see him as one of the few remaining openly left-wing voices in a continent increasingly dominated by right-wing politics.

His opposition to the use of bases is seen by some analysts as an attempt to rally his supporters around an issue that unites the Spanish left.

Sanchez, in power since 2018, heads a minority coalition government that is struggling to pass legislation.

The popularity of his Socialist party has been hit by a series of sexual harassment and corruption scandals ahead of the next general election in 2027.

Many on Spain's right view Sanchez's opposition to Trump as motivated more by domestic politics than a moral compass.

The leader of the main opposition conservative Popular Party, which leads opinion polls, Alberto Nunez Feijoo, accused Sanchez in X of using foreign policy for "partisan" purposes.

The left-leaning daily newspaper El Pais urged Sanchez in an editorial on Wednesday to "resist the temptation" to "exploit the widespread hostility towards Trump in Spanish society to boost his popularity."