This is an action significantly beyond its prior controversial policy to deny US use of jointly-operated military bases, and what has also been a long-running ban on ships transferring arms and ammo to Israel.

Spain's Defense Minister Margarita Robles announced on Monday, "We don't authorize either the use of military bases or the use of airspace for actions related to the war in Iran."

Prime Minister Pedro Sánchez has also confirmed, "We have denied the United States the use of the Rota and Morón bases for this illegal war. All flight plans involving operations in Iran have been rejected. All of them, including those for refueling aircraft." Apparently an exception will be made for emergency landings. But in essence this means no US flyovers by tanker aircraft or bombers will be approved.

Crucially, El Pais - which first broke the news - has also made clear that the airspace ban applies to US aircraft coming from UK and French bases which are involved in the Iran theatre.

"Not only is it prohibiting the use of the military bases in Rota (Cádiz) and Morón de la Frontera (Seville) by fighter jets or in-flight refueling aircraft participating in the attack; it is also denying airspace access to U.S. aircraft stationed in third countries, such as the United Kingdom or France, according to military sources," the Spanish publication says.

Economy Minister Carlos Cuerpo has articulate the government's justification for the move as follows: "This decision is part of the decision already made by the Spanish government not to participate in or contribute to a war which was initiated unilaterally and against international law."

Another important exception is for American warplanes or transport aircraft supporting purely European operations. These planes which are not directly involved in the Middle East operation will be allowed to continue to use Spanish bases.

But ultimately this constitutes a huge inter-NATO rift. It means that American planes are forced to bypass the significant territory of NATO member Spain en route to their targets in the Middle East. President Trump has repeatedly threatened to cut trade with Spain, amid other punitive measures.