Both sides also took aim at shipping traffic, with the US saying it was enforcing a naval blockade while Iran said it targeted vessels that violated its rules on navigating the Strait of Hormuz, the vital waterway for one-fifth of the world’s oil supply.

Oil prices climbed more than four per cent on Friday to their highest level in more than a month, applying political pressure on US President Donald Trump as his Republican Party tries to hold on to power in November congressional elections.

Washington and Tehran have been testing the limits of escalation since their ceasefire agreement collapsed last week, raising the prospect of a return to all-out war.

The US military’s Central Command said it concluded its latest round of attacks by hitting surveillance sites, military logistics infrastructure, underground weapons storage and maritime capabilities.

“US forces employed fighter aircraft, aerial drones, and warships in addition to other assets,” Central Command said in a statement.

“More than 50,000 American service members are operating across the Middle East and remain vigilant, lethal, and ready.”

Iranian media reported on Saturday that several missiles struck power facilities and desalination pumps in the southern Iranian city of Jask, citing a local official. The official said drinking water had been cut off in villages in Jask due to the attack.

The US said its forces redirected four commercial vessels, disabled one, and boarded another to enforce its naval blockade of Iran.

In turn, Iran’s Revolutionary Guards said four vessels violating its rules on shipping traffic were stopped from going through the strait with a combined missile and drone operation.

In addition, Iranian media, citing Iran’s Revolutionary Guards, reported that two oil tankers exploded and caught fire after passing through a mined route south of the strait. The US military labelled that report as false.

Armed men seized another vessel off Yemen, raising concern over security in the Middle East’s other big choke point for oil shipments at the mouth of the Red Sea.

Iran’s state television quoted the Revolutionary Guards as saying that until US “aggression” comes to an end, it will not be possible to export chemical fertilisers or even a “single drop of oil and gas” from the region.

Mohsen Rezaei, an adviser to Iran’s supreme leader, warned on Friday against US escalation or any attempt to seize Iranian territory.

Iran’s army said it struck US military targets in Kuwait and Jordan in response to American attacks, according to a statement carried by the Iranian state broadcaster on Saturday.

In Kuwait, Iranian forces targeted an ammunition depot in the Al-Adiri camp, the headquarters buildings and ammunition depots in the Ali Al-Salem base and several communication bridges.

In Jordan, fuel tanks at the Al-Azraq base were also targeted, the state broadcaster said on Telegram.

Concern over infrastructure

United Nations Secretary General Antonio Guterres was concerned about the escalation, particularly attacks on civilian infrastructure in Iran and across the region,” his spokesperson said.

The US military’s Central Command said its targets included “military logistics infrastructure”, the first time it mentioned infrastructure in more than a week.

Iranian media reported enemy strikes early on Saturday in coastal Hormozgan Province on the Iranian side of the Strait of Hormuz. State TV said three people were killed and eight wounded while two bridges and a road tunnel were damaged.

Iranian media reported explosions heard or strikes carried out in Sirik, Ahvaz, Yazd, Jask and Khorramabad late Friday or early Saturday.

On Friday, Iranian state media said at least five bridges were struck in the south in U.S. attacks. Seven people were reported killed in attacks on bridges in the southern port of Bandar Khamir, where a train station was also hit.

An airport was reported hit further east and away from the coast in Iranshahr, in a province bordering Pakistan.

Trump has threatened to launch broad-based air strikes on Iran’s infrastructure and has also declined to rule out a ground assault on Iran’s coast or islands.

US officials have said attacks on southern Iran are designed in part to give Trump options. Such moves risk provoking Iran to attack the vital infrastructure of vulnerable Gulf states, or having its allies in Yemen further disrupt global energy supplies by attacking shipping from the Red Sea.