"I believe the response should be very strong, very powerful, and that's what this one is," US President Donald Trump told ABC News.
Iran's state media reported that Qeshm island in the Strait of Hormuz was attacked and that a projectile hit was confirmed in the port city of Sirik on the strait. Explosions were heard in nearby Bandar Abbas, the Mehr news agency said.
Trump said the two US pilots involved in the helicopter incident were uninjured.
The Apache was brought down by a one-way Iranian attack drone, according to a US official who spoke on condition of anonymity.
Iran's Foreign Minister Abbas Araqchi did not directly address the helicopter incident, but said Iran 'will leave no attack or threat unanswered' and foreign forces in the region risked being involved in accidents or crossfire.
"To reduce risk, best solution is for them to leave," he said on X.
Iran's state media later cited a military source as saying that no offensive air military operations have been conducted in the Strait of Hormuz in the previous 24 hours.
The source was also quoted as saying that there would be a decisive response in the event of renewed "hostility by the enemy" in response to the helicopter incident.
The latest strikes began at 5pm on Tuesday US time (7am Wednesday AEST) and "the mission is a proportional response to unjustified Iranian aggression", the US military said on X.
Several Iranian air defence systems and radar systems around the Strait of Hormuz were targeted, Axios reported, citing a US official.
Trump told The Wall Street Journal during a phone call the helicopter incident "wasn't a big deal" and stressed that "the pilot is fine".
However, the episode could well add further strain to efforts to broker a peace deal to end the wider Middle East war and reopen Hormuz, a vital conduit for petroleum and other commodities.
Trump has repeatedly said Iran and the US are close to an agreement, though there have been few signs of progress since a tenuous ceasefire took effect in early April.
A US Navy surface drone found and rescued the two crew, after the US Army attack helicopter went down in waters near Oman's coast while on patrol at around 3am on Tuesday US time.
The US military's Central Command gave no reason for the crash. It said the soldiers were rescued after two hours and said they were in stable condition - a more cautious assessment than Trump's description.
In a parallel conflict, Israel struck the historic port city of Tyre in southern Lebanon, killing at least eight people. It was the deadliest strike on the city since fighting erupted in Lebanon in early March, when Hezbollah launched rockets at Israel.
A video verified by Reuters showed debris strewn across a road at the site of the attack.
Israel's refusal to end its campaign against Iran-backed Hezbollah has hindered Trump's efforts to extend a tenuous ceasefire in the wider US-Israeli war with Iran into a durable settlement.
Iran and Israel exchanged airstrikes earlier this week, killing two people in Tehran.
Trump told Axios on Monday he warned Israeli Prime Minister Benjamin Netanyahu not to return to war with Iran: "I said, 'Bibi, you better be careful, or you will be on your own very soon'.
Tehran has long said any peace deal with Washington depends in part on an end to fighting in Lebanon.
In northern Israel on Tuesday, Israeli troops operating in the Ramim Ridge area close to Lebanon's border killed one person in an incident in which they returned fire, the military said.
Israel has never halted its Lebanon campaign, which has killed thousands of people, saying the conflict should be treated separately from any US-Iranian ceasefire. Hezbollah has also continued its attacks.
At the same time, Tehran has continued to block most shipping through the Strait of Hormuz, which before the war carried a fifth of the world's crude oil and liquefied natural gas. Washington has imposed its own blockade of Iranian ports.
