Iran live updates: Trump threatens Iran infrastructure strikes if talks fail

Spain's defense minister says the country has closed its airspace to U.S. planes involved in the Iran war.

Spain had already said the U.S. couldn't use jointly operated military bases in the country for operations related to the conflict.

Defense Minister Margarita Robles said Monday that the same logic applied to the use of Spanish airspace in the conflict.

Spain's government under Prime Minister Pedro Sánchez has been Europe's most critical voice of U.S. and Israeli military actions in the Middle East.

President Donald Trump said in a post to social media on Monday morning that the U.S. is currently engaged in "serious discussions with A NEW, AND MORE REASONABLE, REGIME to end our Military Operations in Iran," but threatened to expand U.S. strikes if the negotiations fail.

"Great progress has been made but, if for any reason a deal is not shortly reached, which it probably will be, and if the Hormuz Strait is not immediately 'Open for Business,' we will conclude our lovely 'stay' in Iran by blowing up and completely obliterating all of their Electric Generating Plants, Oil Wells and Kharg Island (and possibly all desalinization plants!), which we have purposefully not yet 'touched,'" Trump wrote.

"This will be in retribution for our many soldiers, and others, that Iran has butchered and killed over the old Regime's 47 year 'Reign of Terror,'" Trump added.

More than a month into the war with Iran, President Donald Trump told reporters on Air Force One Sunday that negotiations with the country are still ongoing, "directly and indirectly," and that he could "see a deal" with the country coming through "soon."

"I do see a deal in Iran, yeah. Could be soon," he said.

However, he also acknowledged that "it's possible we won't" come to a deal and added, "you never know with Iran."

Asked if he is still considering boots on the ground and if he would consider doing so without Congressional approval, Trump did not reply yes or no, instead insisting that he has "lots of alternatives."

"I just have lots of alternatives. We have tremendous numbers of ships over there. We don't need them all because of, you know, the power," Trump said.

-ABC News' Megan Mistry and Emily Chang

A United Nations peacekeeper was killed over the weekend "when a projectile exploded in a UNIFIL position" in Southern Lebanon, according to the organization. Another peacekeeper was critically injured.

UNIFIL, the U.N. Interim Force in Lebanon, said it does not know where the projectile originated from, and an investigation is ongoing.

"Too many lives have been lost on both sides of the Blue Line in this conflict. There is no military solution. The violence must end," UNIFIL said.

-ABC News' Victoria Beaulé