Iran has attacked US bases in the Gulf region in retaliation for the latest round of US strikes, which came after Donald Trump said he would hit the country "hard".
US Central Command (Centcom) said it had completed its second consecutive day of "self-defense strikes", launched overnight after Trump said Tehran had taken "too long to make a deal" to end the war.
In response, Iran said it had attacked US military bases in Bahrain and Kuwait, the same two targets of retaliatory Iranian strikes conducted the day before.
The escalation of tit-for-tat attacks in recent days has tested a fragile ceasefire agreed between the two countries in April.
After the latest US attack, explosions were heard in cities in the south of Iran, near the Strait of Hormuz, where US forces also hit air defence, radar and other sites in the earlier round of strikes.
In the latest flare-up, Iran's Islamic Revolutionary Guards Corps (IRGC) also said it had struck two oil tankers passing through the Strait of Hormuz, Iranian state media reported, although there was no immediate confirmation.
That came after Iranian state media reported that the Strait of Hormuz was "completely closed to all type of vessel". Centcom, however, said "commercial ships are continuing to transit in and out of the Strait of Hormuz".
Oil prices rose shortly after the closure of the shipping channel and the apparent attack on the ships was announced.
Brent crude oil, seen as the global benchmark, climbed above $95 a barrel after rising by about 2% during morning trade in Asia.
Hours before the US launched its latest attack, Trump had warned: "We hit them hard yesterday and we're going to hit them hard again today."
Trump wrote on Truth Social that Iranian leaders have "taken too long to negotiate a deal".
US Defence Secretary Pete Hegseth said Iran had been given a chance to make a deal but had not taken it, adding that bombs would be "dropping on key facilities" in the country.
The US president added that Iran would be attacked again if no peace deal was secured.
Iranian President Masoud Pezeshkian said Iran "will stand firm against any pressure or threat". The Iranian foreign ministry earlier accused the US of "damaging the diplomatic process through the contradictory messages it sends".
In April, the US and Iran agreed a ceasefire that was initially meant to last for two weeks. Both sides have since exchanged intermittent fire, without returning to full-scale hostilities.
However, recent efforts to broker negotiations between Washington and Tehran have stalled and attacks have ramped up.
This week, a US helicopter was downed in an attack that was blamed on Iran. The IRGC responded by targeting US bases across the Middle East.
In a statement on X, UN Secretary General António Guterres said the Middle East was "being pulled deeper into crisis", and recent attacks meant "the ceasefire is more like a lesser-fire".
"We should not minimize the risks of lesser fire becoming full fire. All parties must work towards a diplomatic settlement. No more attacks. No more excuses," he said in a statement.
