US forces have bombed Iran's south and west after President Donald Trump said Tehran would pay dearly for the deaths of American soldiers, while Iran has targeted US sites in Bahrain, Kuwait and Jordan on Tuesday and a tanker was hit in the Strait of Hormuz.
The exchanges came a day after Yemen's Iran-aligned Houthis said they would impose a naval blockade on Saudi Arabia, opening a potential new front in the war and raising the threat to global energy supplies and trade beyond the Gulf.
Shipping companies loading or discharging cargo at Saudi ports could be targeted "in any location" by Houthis, according to an email sent to companies on Monday and seen by Reuters.
Despite the escalating cycle of attacks that has all but wrecked an interim peace agreement signed in June, signs that Tehran and Washington want to resume diplomacy kept oil prices in check.
US Central Command said it had hit Iranian military command centres, maritime capabilities, missile and drone launch sites, and air defence systems in its latest round of strikes.
Explosions were heard around the city of Shiraz in southern Iran.
Konarak and Chabahar on the southern coast and the city of Khorramabad and a civilian site outside the city of Abdanan, both in the west, also came under attack, according to state media.
Iran launched renewed attacks across the Gulf, where recent strikes on desalination facilities have raised concerns about water shortages and underscored the growing threat to civilian infrastructure.
Attacks on Kuwaiti power generation and water desalination plants on Monday caused fires that had been extinguished by Tuesday with repairs under way, authorities said.
Iran's Revolutionary Guards said they targeted infrastructure in Bahrain belonging to US tech company Amazon in retaliation for what they described as a US strike on the construction site of Iran's planned Darkhovin nuclear power plant.
Iranian state media reported that Iranian forces also targeted accommodation facilities used by US military personnel at Bahrain's Sheikh Isa Air Base.
The Iranian army said it launched drone attacks against three US military bases in Kuwait on Tuesday.
The Guards said they attacked a US military site in Jordan, while Jordan said its forces intercepted and destroyed five Iranian drones.
The maritime security agency UKMTO said on Tuesday a tanker in the Strait of Hormuz reported being struck by an unknown projectile, forcing its crew to abandon the vessel and board a lifeboat.
Also on Tuesday, Iran's Revolutionary Guards said two oil tankers had caught fire after explosions while attempting to transit the southern route of the strait.
It was not immediately clear when those incidents took place.
Iran had been pressing the Houthis to close the Bab el-Mandeb gateway to the Red Sea if the US continued to attack Iranian power infrastructure - putting two of the world's most vital energy arteries at risk.
A senior Iranian official told Reuters on Monday that Tehran had received a proposal from mediators for a 10-day ceasefire in efforts to salvage the interim deal, intended to pave the way to a lasting agreement to end the war that began on February 28 with US-Israeli attacks on Iran.
Iranian Interior Minister Eskandar Momeni has arrived in Islamabad for further talks after asking Pakistan to resume its mediation role in the conflict.
The latest phase of fighting has proved to be among the deadliest of the conflict for US forces. US troop deaths rose to 17 at the weekend.
Trump, under mounting pressure at home over rising petrol prices since the war began, said the latest US strikes on Iran were avenging the deaths of American service members.
"Every time Iran kills an American Soldier they will pay for that killing many times over!" Trump wrote on Truth Social on Monday.