The conflict has killed thousands of people, spread to neighbouring nations and hit the global economy since the United States and Israel launched strikes on February 28, after talks about Tehran's nuclear program failed to yield a deal.
"The IDF has just begun a wave of strikes against the infrastructure of the Iranian terror regime in the heart of Tehran," a spokesperson for the Israeli Defence Forces said on Friday, without providing details.
Bahrain, Kuwait and the United Arab Emirates said they were dealing with missile attacks in the early hours of Friday, following days of Iranian strikes on regional energy infrastructure that have roiled global markets.
Energy prices jumped on Thursday after Iran responded to an Israeli attack on a major gas field by hitting Qatar's Ras Laffan Industrial City, which processes around a fifth of the world's liquefied natural gas, causing damage that will take years to repair.
Saudi Arabia's main port on the Red Sea, where it has been able to divert some exports to avoid Iran's closure of the Gulf's exit point, the Strait of Hormuz, was also attacked on Thursday.
But oil prices fell on Friday as leading European nations and Japan offered to help secure safe passage for ships through the Strait of Hormuz, the conduit for a fifth of the world's oil supplies, and the US outlined moves to boost oil output.
The strikes on regional energy facilities underscored Iran's continued ability to exact a heavy price for the US-Israeli campaign, and the limits of air defences in protecting the Gulf's most valuable and strategic energy assets.
Trump said he had told Israeli Prime Minister Benjamin Netanyahu not to repeat the attack on energy infrastructure.
"I told him, 'Don't do that', and he won't do that," he told reporters in the Oval Office on Thursday.
Netanyahu later said Israel had acted alone in the bombing of Iran's South Pars gas field and confirmed that Trump had asked Israel to hold off on such attacks.
Iran is being "decimated" and no longer had the capacity to enrich uranium or make ballistic missiles, but a revolution in the country would require a "ground component," Netanyahu said, without elaborating.
Britain, Canada, France, Germany, Italy, the Netherlands and Japan issued a joint statement expressing "our readiness to contribute to appropriate efforts to ensure safe passage through the Strait".
They also promised "other steps to stabilise energy markets, including working with certain producing nations to increase output".
There was little indication of any immediate move. German Chancellor Friedrich Merz reiterated any contribution to securing the strait would come only after hostilities ended.
Trump has said the US did not know about Israel's bombing of Iran's South Pars gas field. However, three Israeli officials said the operation had taken place in consultation with the United States, but was unlikely to be repeated.
Director of National Intelligence Tulsi Gabbard told a US congressional committee that American and Israeli goals differed.
The Israeli government has been focused on disabling the Iranian leadership while Trump's objectives are to destroy Iran's ballistic missile launching and production capability and their navy, Gabbard said.
Iran's military said strikes on Iran's energy infrastructure had led to "a new stage in the war" in which it had attacked energy facilities linked to the United States.
"If strikes (on Iran's energy facilities) happen again, further attacks on your energy infrastructure and that of your allies will not stop until it is completely destroyed," Iranian military spokesman Ebrahim Zolfaqari said, according to state media.
Israeli media reported that an Iranian strike hit oil facilities in Israel's port of Haifa, causing damage but no casualties.
