The US military has carried out strikes on Iran, targeting a military site in Bandar Abbas, a strategic port city.
In response, Iran's Islamic Revolutionary Guard Corps (IRGC) said it had targeted a US air base, without providing details of its location.
Kuwait, which hosts a US air base, said its air defences were intercepting "hostile missile and drone threats", but did not specify where they were coming from.
The renewed hostilities threaten a fragile ceasefire between the US and Iran.
It is the second time in three days that the US has attacked targets in Iran - saying that the strikes were conducted in self defence.
The site in Bandar Abbas was struck as it was about to launch a fifth drone, US Central Command (Centcom) said. Iranian media reported that explosions were heard to the east of the city.
Centcom described its actions as "measured, purely defensive, and intended to maintain the ceasefire".
It also said its forces shot down four Iranian one-way attack drones "that posed a threat around the Strait of Hormuz".
Iran condemned the strikes as "a grave violation of the ceasefire" and vowed that the Iranian government "will not leave any act of hostility unanswered."
Earlier this week, the US confirmed a previous round of "self-defence" strikes on southern Iran on Monday in which they targeted Iranian missile sites and boats attempting to lay mines in the Strait, where thousands of commercial tanker ships are stranded as a result of the conflict.
Centcom said those strikes were designed "to protect our troops from threats posed by Iranian forces".
The US also imposed sanctions on the "Persian Gulf Strait Authority" – the Iranian body tasked with collecting payments from ships travelling through the Strait of Hormuz.
Any ships that pay the authority could also be "exposed to the risk of sanctions", the US Treasury Department said in a statement.
One-fifth of the world's liquefied natural gas and oil normally pass through the shipping channel, and its closure has impacted global fuel trade.
Iran's foreign ministry spokesman Esmaeil Baqaei said on Monday that Tehran was collecting fees for "navigational services" and it would continue to manage traffic through the waterway.
US Treasury Secretary Scott Bessent described it as the "Iranian military's latest attempt to extort global maritime trade" and "proof" Iran is "desperate for cash".
The IRGC also said on Tuesday that it had downed a US drone and fired at a fighter jet and another drone that entered Iranian airspace, but did not specify when.
Protracted negotiations have been taking place to end the three-month war that has choked traffic in the Strait of Hormuz and caused global energy prices to shoot up.
During a cabinet meeting on Wednesday, US President Donald Trump said that Iran is "negotiating on fumes", insisting that his war strategy will not be impacted by November's US midterm elections.
"Maybe we have to go back and finish it, maybe we don't," he said.
During that meeting, the president also urged Gulf nations to sign on to the Abraham Accords to normalise relations with Israel.
Israel launched the war against Iran alongside the US on 28 February and is also embroiled in a war with Iranian-backed Hezbollah in Lebanon.
Trump has threatened to resume a large-scale bombing campaign if Iran does not agree to his terms.
While Trump struck an optimistic note over the weekend, saying that a peace deal with Iran had been "largely negotiated", by Wednesday's cabinet meeting, he said that the US is "not satisfied".
He said Tehran was "very much intent" on reaching an agreement to end the conflict, but added "so far they haven't gotten there", repeating Washington's willingness to resume strikes if one is not reached.
His remarks came after Iranian state TV reported what it said were details of a draft agreement, which included reopening the Strait of Hormuz and the withdrawal of US forces from the region.
The White House branded the text a "complete fabrication".
Both sides signalled progress had been made towards a deal late last week, prompting speculation an announcement was close.
However, Tehran soon cautioned a deal was "not imminent" while Trump said he had instructed his negotiators "not to rush into" one.
Speaking to reporters at a cabinet meeting on Wednesday, the US president said: "They just want to make a deal - I don't think they have a choice."
Trump also said: "Iran is very much intent, they want very much to make a deal.
"So far, they haven't gotten there and we're not satisfied with it, but we will be. Either that or we'll have to just finish the job."
