MADRID, March 30 (Reuters) - Spain has closed its airspace to U.S. planes involved in attacks on Iran, a step beyond its previous denial of use of jointly-operated military bases, Spanish newspaper El Pais reported on Monday, citing military sources.

The closure of its airspace, which forces military planes to bypass NATO member Spain en route to their targets in the Middle East, does not include emergency situations, El Pais added.

The Spanish Ministry of Defence did not immediately reply to a request for comment.

"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," Economy Minister Carlos Cuerpo said during an interview with radio Cadena Ser when asked if the decision to close Spain's airspace could worsen relations with the United States.

Spanish Prime Minister Pedro Sanchez has been one of the most vocal opponents of the U.S. and Israeli attacks on Iran, describing them as reckless and illegal.

President Donald Trump has threatened to cut trade with Madrid for denying the U.S. use of Spain's bases in the war.

(Reporting by Paolo Laudani and Emma Pinedo; editing by Charlie Devereux and Gareth Jones)