Pedro Sanchez
© Pool Moncloa/Borja Puig de la BellacasaSpanish Prime Minister Pedro Sanchez. The Pentagon is in damage control to salvage Operation Prosperity Guardian, as most NATO members have balked at the idea of joining the US-led endeavor
Pentagon officials are pressuring Spain to "reconsider its refusal" to take part in the Red Sea Operation Prosperity Guardian (OPG) and have set an 11 January deadline for Madrid to "join with a ship or, at least, with personnel stationed in the area," according to informed sources who spoke with Spanish daily El Confidencial.

As the US-led alliance struggles to make an impact against the pro-Palestine actions of the Yemeni armed forces, the Chairman of the Joint Chiefs of Staff, General Charles Brown, on Monday contacted his Spanish counterpart, Admiral Teodoro Lopez Calderon, to reiterate Washington's "desire to work with all nations that share an interest in defending the principle of freedom of navigation and ensuring safe passage for global shipping."

"Spain is a vital NATO ally and shares a long and strategic relationship with the US," says the US navy readout of the phone call.

In parallel to this conversation, which was made public, a separate phone call took place between the US Secretary of the Navy, Carlos del Toro, and the Spanish ambassador in Washington, Santiago Cabanas, during which the Pentagon official "in much more direct language" pressed Madrid to take part in the naval coalition in support of Israel.

"[Del Toro] gave [Cabanas], at the end of the conversation, a kind of ultimatum: He wants to know, at the latest on Thursday the 11th, if Spain corrected its decision," El Confidencial reports.

Spain has been the most vocal NATO member to reject being named part of this "coalition of the willing," vetoing a vote at the EU that called for support of the coalition and making it clear that its forces committed to Operation Atalanta - a counter-piracy operation off the Horn of Africa and in the Western Indian Ocean - would not join OPG.

The veto by the Spanish mission to Brussels was a direct order from Prime Minister Pedro Sanchez, according to local reports.

This public pushback prompted US President Joe Biden to contact Sanchez in late December to discuss the crisis in Gaza and warn him about the "Houthi threat" in the Red Sea.

Nonetheless, Sanchez maintained his decision against joining OPG and also refused to join a statement that the US and its main European and Asian allies published on 3 January in which they issued a collective warning to Yemen. France did not subscribe to this text either.

While Madrid has not publicly explained their reasoning for refusing Washington's demands, El Confidencial reports that authorities believe that, if Spain were to join OPG, this "would be ... a way to relieve pressure on Israel and reduce the possibilities of reaching a definitive ceasefire in Gaza."