Iran’s Islamic Revoluationary Guard Corps has reportedly warned the U.S. that it considers retaliatory strikes "legitimate and definite" should the U.S. violate an ongoing ceasefire agreement, as tensions once again intensify in the Middle East, denting hopes for an imminent peace deal.

Media reports citing Tasnim, a news agency closely linked to the IRGC, added that Iranian forces had fired upon an American drone and "drove off" an fighter jet.

Earlier, the U.S. military said it had conducted fresh strikes in southern Iran against missile launch sites and mine-laying boats, according to reports quoting U.S. Central Command. 

The strikes were "defensive" in nature and did not indicate that a ceasefire with Iran had ended, reports said, citing CENTCOM. The development was first reported by Fox News. 

"U.S. forces conducted self-defense strikes in southern Iran today [...] Targets included missile launch sites and Iranian boats attempting to emplace mines," CENTCOM spokesperson Tim Hawkins told U.S. media. 

Hawkins stressed that the strikes "do not indicate ceasefire is over," noting that "U.S. Central Command continues to defend our forces while using restraint."  

Shortly after the attacks, U.S. Secretary of State Marco Rubio said that a deal to reopen the Strait of Hormuz could "take a few days," but vowed that the strait was going to reopen "one way or another." 

Recent optimism that Washington and Tehran may be approaching a lasting agreement to end their nearly three-month old war eased in the wake of the strikes.

Over the weekend, news reports said both sides were close to a framework deal to extend the ceasefire and unblock the Strait of Hormuz, while President Donald Trump later talks were proceeding "nicely." However, Trump also warned of a resumption and escalation in fighting should a deal not be reached. 

It was not immediately clear if the latest round of strikes had destabilized those negotiations.

Trump also said on Monday evening that Iran’s enriched uranium will either be turned over to Washington or destroyed "in place or, at another acceptable location."  The president has repeatedly said Iran must hand over its enriched uranium holdings as part of any peace agreement with Washington. 

Trump has repeatedly touted preventing Iran from building a nuclear weapon as one of the main objectives of the joint U.S.-Israeli assault against Iran, which began in late February. But media reports have suggested that Iran has largely rejected these demands.