"US forces began launching strikes against Iran at 8pm ET today" (10am Thursday AEST), US Central Command said in a statement on Wednesday.
"The strikes are a powerful response to yesterday's attempted Iranian attacks on US forces based in the Middle East."
Earlier on Wednesday, a drone hit a US-owned gas storage tanker at Egypt's Mediterranean port of Damietta, British maritime security firm Ambrey said in an initial assessment, while US and Saudi forces launched strikes against Iran-aligned groups in eastern Iraq and Iran fired missiles at US troops in Jordan.
The latest strikes in Iraq and Egypt threatened to draw more Middle Eastern countries into the conflict, after the Iran-aligned Houthis in Yemen last week declared a naval blockade on Saudi Arabia.
The US strikes in Iran on Wednesday followed President Donald Trump's vow earlier in the day to retaliate against Iran for firing on US troops.
"So it's our turn," Trump told reporters at the White House, promising to "hit them very hard" even as he again said Washington would continue to aim for a peace deal with Tehran.
Iran confirmed overnight that it had fired on US bases in Jordan and at ships in the Strait of Hormuz, and also spurned an Omani proposal to jointly manage the strait, a critical global shipping route for oil and gas.
The joint US-Saudi attacks marked the first time Riyadh has publicly joined strikes alongside Washington.
Iraq's Popular Mobilisation Forces, powerful Iran-backed paramilitary groups incorporated into the Iraqi security forces, said at least 20 members were killed and 32 wounded in US-Saudi strikes targeting several bases across Iraq.
Iraqi men shouted "Death to America!" as they carried the bodies of slain fighters in body bags.
Washington and Riyadh said they struck Iran-backed armed groups in Iraq in retaliation for drone attacks on Saudi oil targets launched from Iraq.
After the joint attacks, Saudi Arabia's defence minister met with Vice President JD Vance in Washington on Wednesday to urge the Trump administration not to escalate the conflict further by attacking Yemen's Houthis and carrying out additional strikes against the Iran-aligned militias in Iraq, two sources told Reuters.
US officials have privately cautioned that resuming major combat operations against Iran would carry risk given the negative impact on stocks of munitions.
The strikes on Iraq expose a dangerous rift in that volatile country. The Shi'ite-led government is one of the few in the world to balance close military and diplomatic ties with both Tehran and Washington, but those divided loyalties are a constant source of tension and frequent domestic unrest.
The Iraqi presidency denounced the strikes on the paramilitaries as "an unacceptable attack and a flagrant violation of Iraq's sovereignty", while also calling for a halt to attacks by armed groups against Iraq's neighbours.
Hours before launching the attacks on Iraq, the US military said its air defences had averted a surprise Iranian attack on US troops in the region.
Jordan's military said it had shot down five Iranian missiles. US bases in Jordan have lately become primary Iranian targets, where three US service members were killed this month in the worst US losses since March.
Iran's Revolutionary Guards said they had fired several ballistic missiles at US military installations in Jordan, and had struck three tankers that were attempting to transit through the Strait of Hormuz along an unauthorised route.
