Days into the US and Israel's joint military strike on Iran, leaders from several major European nations have expressed their disagreements, if not objections, to the unilateral move.

"A logic of violence, as we are seeing, only leads to a spiral of violence, and unilateral military actions outside the United Nations Charter, outside any collective action, have no clear objective. Europe must defend international law, de-escalation, and negotiation," Spanish Foreign Minister Jose Manuel Albares Bueno said on Monday, as his government refused to allow its military bases, which are operated jointly with the US but under Spanish sovereignty, to be used for attacks on Iran.

Spain is a US ally that openly condemned the latter's strikes against Iran, as Prime Minister Pedro Sanchez on Saturday called it "unilateral military action", as well as an "unjustified" and "dangerous military intervention" outside the bounds of international law.

On Monday, flight tracking website Flightradar24 showed that 15 US aircraft had already left the Rota and Moron military bases in southern Spain since the attacks were launched. They were relocated to other bases.

US President Donald Trump threatened to impose a full US trade embargo on Spain on Tuesday in response to the refusal.

"Spain has been terrible," Trump told reporters during a meeting with German Chancellor Friedrich Merz. "We're going to cut off all trade with Spain. We don't want anything to do with Spain."

Sanchez on Wednesday doubled down on his opposition to the attack on Iran by the US and Israel, warning that the conflict risked triggering a major global disaster.

"We're not going to be complicit in something that's bad for the world, nor contrary to our values and interests simply to avoid reprisals from someone," Sanchez said in a televised address to the nation.

Sanchez said governments existed to improve people's lives and lashed out at leaders who "use the fog of war to hide their failure" at home.