President Donald Trump said the US was considering winding down its military operation against Iran, as Iran and Israel traded attacks on Saturday and Iranian media said the nuclear enrichment facility in Natanz had been attacked.
In a social media post, Trump said the US was close to meeting its goals but insisted that other countries should take the lead in policing the vital shipping lane of the Strait of Hormuz, whose near-closure threatens a global energy shock.
Trump has suggested the war could wind down as the Iranian threat was being eliminated, while at the same time US Marines and heavy landing craft head to the region on a mission whose goals are not immediately clear.
"We are getting very close to meeting our objectives as we consider winding down our great Military efforts in the Middle East with respect to the Terrorist Regime of Iran," Trump said on social media.
"The Hormuz Strait will have to be guarded and policed, as necessary, by other Nations who use it - The United States does not!" he added. "If asked, we will help these Countries in their Hormuz efforts, but it shouldn’t be necessary once Iran’s threat is eradicated."
Trump had also accused NATO allies, which have not been consulted about the war, of cowardice over their reluctance to help open the strait.
Iranian gas supplies to Iraq reportedly resumed after flows were halted by an Israeli attack on Iran's main gas field, South Pars, on Wednesday.
As the fighting continued, Iranian media said US-Israeli forces had attacked the Shahid Ahmadi-Roshan Natanz enrichment complex on Saturday morning. Technical experts found that no radioactive leaks had occurred and nearby residents were not at risk. Israel said it was unaware of such a strike while the head of the International Atomic Energy Agency (IAEA) said it was investigating.
Russia called it, "a blatant violation of international law."
Iran fired two ballistic missiles towards the US-British military airport on the island of Diego Garcia, 3,800 kilometres (2,400 miles) away in the Indian Ocean but did not hit the base, the Wall Street Journal reported.
A source at Britain's defence ministry said the attack had occurred before the government gave specific authorisation on Friday for the US to use British military bases to carry out strikes on Iranian missile sites.
Natural gas prices in Europe surged as much as 35 per cent this week as Iran and Israel hit some of the region's most important gas infrastructure. The European Union urged members to lower gas-storage targets and start refilling reserves gradually to curb demand, the Financial Times reported on Saturday.
The Strait of Hormuz, conduit for around a fifth of global oil and liquefied natural gas supplies, has been effectively closed to most shipping. Leading allies of the US from Europe as well as Japan and Canada have pledged to join "appropriate efforts" to ensure safe passage through the strait, but Germany and France have complained that fighting must stop first.
Foreign Minister Abbas Araqchi told the Kyodo news agency that Iran was ready to let Japan-related vessels pass through the strait, which carries around 90 per cent of Japan's oil imports.
Muslims celebrated Eid al-Fitr on Friday to end the fasting month of Ramadan and Iranians marked Nowruz, the Persian New Year. Iran's new supreme leader, Ayatollah Mojtaba Khamenei, marked the occasion with a message of defiance.
Khamenei - who did not appear at Eid prayers and has not been seen in public since the initial Israeli attack, which killed his father and predecessor, Ayatollah Ali Khamenei - said in his statement that Iranians had responded with unity and resistance and "dealt a disorienting blow to the enemy".
(Reporting by Phil Stewart and Idrees Ali in Washington, Andrew Mills in Doha and Timour Azhari in Riyadh; Additional reporting by Reuters bureaux; Writing by Tom Hogue and Matthias Williams; Editing by William Mallard)