The escalation in hostilities highlighted threats to the tenuous ceasefire between the US and Iran that took effect in early April, dampening hopes for a peace deal and sending oil prices surging again.

The US official, who requested anonymity to speak candidly about military operations, told Reuters the military shot down four Iranian attack drones and struck a ground control station in the port city of Bandar Abbas that was about to launch a fifth drone.

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

The Islamic Revolutionary Guard Corps said it targeted a US base in response to what it described as an early morning US attack near Bandar Abbas airport, Tasnim news agency reported. The IRGC said they targeted the US airbase from which the attack on the control station near Bandar Abbas was launched.

Kuwait – which hosts a large US base – said it was responding to missile and drone attacks without saying where the attacks were coming from.

Israel, which has been fighting Iran-backed Hezbollah rebels in southern Lebanon, also reported sounding sirens regarding hostile aircraft activity in northern Israel.

Oil prices, having fallen more than 5% on Wednesday, rebounded after reports of the escalation in hostilities. US crude futures gained more than 3%, while stocks fell and the dollar rose.