US President Donald Trump has said that the ceasefire with Iran "is over", after Washington launched strikes on the country overnight to which Iran responded by targeting US bases in the Gulf.

"As far as I am concerned, it's over", Trump said at a NATO summit in Ankara on Wednesday morning. He was responding to a question on whether the truce with Iran was now finished.

"I don't want to deal with them any more, they're scum," Trump continued. "They're scum, they're sick people, they're led by sick people, and they're vicious, violent people. And if they had a nuclear weapon, they'd use it.

"As far as I'm concerned, it's over."

Trump said he would speak to businessman-turned-negotiator Steve Witkoff and his son-in-law Jared Kushner, who have been dealing with the Iranians, but insisted it was up to Tehran to return to the table.

"As far as I'm concerned, it's just a waste of time dealing with them. They're liars."

Trump accused the Iranians of repeatedly misrepresenting what had been agreed in the ceasefire that Washington and Tehran signed on June 17.

"Everyone's agreed, no nuclear weapon. We make a deal. They go outside, joke to the press, they say we never even talked about it. There's something wrong with them, they're cuckoo," Trump added.

The US had launched strikes on Iran just a few hours earlier, hitting more than 80 targets, according to US Central Command, which said the attacks were conducted in response to Tehran's attacks on three ships in the Strait of Hormuz.

"US forces struck Iranian defence systems, command and control networks, coastal radar sites, anti-ship missile capabilities, and more than 60 Islamic Revolutionary Guard Corps small boats in and near the strait," the US military said in a statement posted to X.

The overnight strikes were "absolutely necessary", NATO chief Mark Rutte said on Wednesday as the alliance began its meeting in Ankara.

"I think it was absolutely necessary because when you have a ceasefire and Iran is basically violating the ceasefire - we see what happened yesterday with ships being attacked - I think it is totally crucial that the US forcefully react," AFP reported.

Iran immediately warned Washington it would “take whatever measures it deems necessary," raising the risks that an interim agreement in the war halting fighting could break down, putting the wider Middle East again at risk of a wider conflict.

Bahrain, home to the US Navy's 5th Fleet, sounded its missile alert sirens Wednesday morning after the American attack on Iran.

Meanwhile, the Kuwaiti army said "Kuwaiti air defenses are currently engaging hostile missile and drone attacks," in a post on X, without saying where they were coming from.

"The General Staff of the Army notes that any explosions heard are a result of air defense systems intercepting hostile attacks."

CENTCOM said American forces launched the strikes “to impose heavy costs for targeting and attacking commercial shipping crewed by innocent civilians in an international waterway.”

It said it hit Iranian targets including air defence systems, radars and over 60 small boats used by Iran’s paramilitary Revolutionary Guard.

The US military remains “postured and prepared to hold Iran accountable when the agreement is not adhered to or obeyed,” it added, saying this round of attacks had ended.

Iran's foreign ministry accused the United States of repeatedly violating the memorandum of understanding agreed between the two sides and threatened retaliation.

“The era of bullying and extortion is over,” Iran's Parliament Speaker Mohammad Bagher Ghalibaf wrote on X. “It leads nowhere. We don’t fold.”

Iranian state media reported the sound of explosions in Bandar Abbas, Qeshm and Sirik, as Iran's central military command warned it “will respond decisively to this aggression and terrorist act."

“Under no circumstances will (the Iranian armed forces) allow interference in the affairs of the Strait of Hormuz, nor will they permit others to manage it,” it said.

A similar spate of Iranian attacks on shipping and US retaliatory strikes occurred late last month — which drew Iranian attacks on Bahrain and Kuwait.

The US also revoked a licence that authorised the sale of Iranian oil as part of the interim deal following the attacks on shipping.

One tanker was travelling off the coast of Oman when it was hit and caught fire, the United Kingdom Maritime Trade Operations centre said, adding that the other two ships sustained some damage, but no one was injured, and both continued on their way in the Strait of Hormuz.