US and Iranian forces exchanged heavy missile and drone strikes, with Tehran targeting US facilities across the Gulf and saying it had once again closed the strategic Strait of Hormuz, sending oil prices higher.
Iran's Revolutionary Guards said on Monday they had targeted US military facilities in Bahrain and Kuwait, destroyed radar systems in Oman, and struck fuel tanks and ammunition depots at Prince Hassan Air Base in Jordan in response to another wave of US strikes.
The attacks were the latest in a series of strikes and counter-strikes as Iran sought to assert control over shipping through the Strait of Hormuz. However, the latest barrage marked a significant escalation in both intensity and geographical reach.
The US military said it had struck Iranian air defence systems, coastal radar sites, missile and drone capabilities, and small boats using aircraft, naval vessels and drones during operations on Sunday.
The renewed violence has cast further doubt on the future of an interim US-Iran agreement signed last month, which aimed to reopen the strait and end the war after a further 60 days of negotiations.
In a brief telephone interview with Reuters on Sunday afternoon, US President Donald Trump referred to the weekend's strikes on Iran, saying: "We're beating them up."
Over the past week, Trump has repeatedly said he considers the ceasefire to be over, while leaving the door open to further negotiations.
Iran's top negotiator, Mohammad Baqer Qalibaf, wrote on X on Sunday: "The era of one-sided deals is OVER. We told you: keep your word or pay the price. Reality is knocking."
The war launched by the United States and Israel against Iran on 28 February has destabilised the Gulf, where Iran has targeted US military bases across the region. Tehran's effective blockade of the Strait of Hormuz has driven up energy prices and fuelled global inflation.
In a statement on Monday, the Revolutionary Guards said the only way to restore normal shipping through the strait was for the United States to end its military operations in the waterway, warning that "continued interference could lead to greater incidents in the global oil and gas sector."
Brent crude rose 4.3% to $79.31 a barrel on Monday, although it remained well below the highs reached earlier in the conflict.
Higher fuel prices, particularly for petrol, are politically sensitive for Trump ahead of November's congressional elections.
US officials said around 20 vessels had been escorted through the strait over the previous 24 hours, although ship-tracking data showed little commercial traffic moving through the waterway.
Iran has sought to establish a permanent system for collecting fees from vessels using the Strait of Hormuz, which carried around one-fifth of the world's oil and liquefied natural gas shipments before the war, and has warned ships not to transit without its authorisation.
Late on Saturday, Tehran said it had closed the waterway after firing a warning shot that struck a vessel travelling on what it described as an unauthorised route. On Sunday, it said it had disabled a second vessel.
Iran's newly established Persian Gulf Strait Authority said on Sunday that passage through the strait was currently impossible because of the "recent illegal movements of the United States military forces in the region". It said permits would be issued again "as soon as stability and calm are restored".
The United States, which revoked a sanctions waiver permitting sales of Iranian crude on Tuesday following earlier attacks on shipping, said its forces remained positioned to safeguard freedom of navigation despite what it described as Iranian "aggression, harassment, threats and arbitrary declarations".
"Iran does not control the strait. Traffic is flowing," it said.
The US Navy-led Joint Maritime Information Center reiterated its guidance that, despite the severe security threat, an expanded southern route near Oman remained open for two-way traffic.
On Saturday, US Central Command said American forces had struck 140 Iranian military targets and that more than 300 targets had been hit over three nights this week "to degrade Iran's ability to attack civilian mariners and commercial vessels freely transiting the strait".
At the weekend, Iran's Revolutionary Guards said they had destroyed a command-and-control centre and drone hangars in Jordan, targeted a US radar site and later rocket-launcher systems in Kuwait, attacked US aircraft carrier support and refuelling platforms in Oman, and destroyed a jet maintenance centre and command facility in Qatar.