The fragile cease-fire between the United States and Iran came under renewed strain early Thursday after both sides exchanged attacks near the Strait of Hormuz, raising fresh fears that the conflict could spiral again despite ongoing negotiations aimed at ending the war.

A U.S. official said American forces carried out what were described as “purely defensive” strikes against an Iranian drone control position in the southern port city of Bandar Abbas after intelligence indicated preparations for another attack. According to the official, U.S. forces shot down four Iranian drones and struck a launch site that was preparing to deploy a fifth aircraft near the strategic waterway.

“These actions were measured, purely defensive, and intended to maintain the cease-fire,” the official said.

Iran quickly responded. The Islamic Revolutionary Guard Corps (IRGC) said it targeted the U.S. air base linked to the operation near Bandar Abbas airport, escalating tensions around one of the world’s most sensitive maritime corridors.

Iranian media also reported explosions around Bandar Abbas, the capital of Hormozgan province and a major military and naval hub overlooking the Strait of Hormuz, a route that carries roughly one-fifth of global oil and liquefied natural gas shipments.