Spain's Prime Minister Pedro Sanchez on Wednesday repeated his firm opposition to the escalating conflict in the Middle East triggered by the joint US-Israeli attack on Iran last weekend.

Sanchez is the only major European leader to have condemned the US-Israeli attacks on Iran.

His opposition to the large-scale military operation has drawn the ire of US President Donald Trump, who on Tuesday said he would slash trade with Spain over the Spanish government's position.

In a televised address on Wednesday, the Socialist prime minister said, "This is how ​humanity's great disasters start ... You cannot play Russian roulette with the destiny ​of millions." 

"The position ​of the Spanish government can be summarised in four words: 'No to the war,'" Sanchez continued, adding that the stance was "consistent and coherent" with its approach to the conflicts in Ukraine and in Gaza.

"We're not going to be ​complicit in something that is bad for the world, nor contrary to our ​values and interests, ‌simply to avoid reprisals from someone," the prime minister said, in an apparent reference to Trump's trade threats.

Sanchez pointed to the lessons of the US invasion of Iraq in 2003, which destabilized the region, triggered a rise in Islamist terrorism and caused energy prices to soar.

Sanchez had already previously denounced the US-Israeli bombings of Iran, calling them illegal and reckless. He has also refused to allow the US to use air and naval bases in southern Spain for the campaign against Iran.

Spain was also one of the few European countries to consistently condemn Israel over its war in Gaza.