Washington has dispatched thousands of Marines to the Middle East in the month-old war.
The first of two contingents arrived on Friday on an amphibious assault ship, the US military said on Saturday.
The Pentagon was preparing for weeks of ground operations in Iran, possibly involving raids by Special Operations and conventional infantry troops, The Washington Post reported on Saturday.
The report said it was not known whether President Donald Trump would approve plans for deploying ground troops.
The war, launched on February 28 with US and Israeli strikes on Iran, has spread across the Middle East, killing thousands and hitting the world economy with the biggest-ever disruption to global energy supplies.
Secretary of State Marco Rubio said on Friday the US could achieve its aims without ground troops but it was deploying some to the region so Trump would have "maximum" flexibility to adjust strategy.
Pakistan, a potential mediator between Washington and Tehran, will host two days of talks from Sunday with the foreign ministers of Saudi Arabia, Turkey and Egypt, seeking ways to ease regional tensions, a day after Iranian President Masoud Pezeshkian spoke to Pakistan's Prime Minister Shehbaz Sharif.
The Israeli military said on Sunday it had targeted Tehran's weapons manufacturing infrastructure, including dozens of storage and production sites.
Five people were killed in a strike on a pier in the southern port city of Bandar-e-Khamir that also destroyed two vessels, Iranian state media reported on Sunday.
Israel also hit targets in Lebanon, resuming its war against Iran-backed Hezbollah, killing three Lebanese journalists and a Lebanese soldier, Lebanon's Al Manar TV reported.
A follow-up strike on the rescue workers sent to assist them also caused fatalities.
Israel's military said it had targeted one of the journalists, accusing him of being part of a Hezbollah intelligence unit and saying he had reported on locations of Israeli soldiers.
Early on Sunday, it said one of its soldiers had been killed during combat in Lebanon.
Iran kept up its attacks on Israel and several Gulf states.
Air defences shot down a drone near the residence of the leader of the Iraqi Kurdish ruling party, Masoud Barzani, in Erbil, security sources told Reuters on Sunday.
Another drone attack on Saturday had targeted the home of the president of Iraq's Kurdistan region.
The Houthis carried out a second strike on Israel, Houthi military spokesperson Yahya Saree said, vowing more to come.
The attacks point to a potential new threat to global shipping, already hit by the effective closure of the Strait of Hormuz, a conduit for about one-fifth of global oil and liquefied natural gas supplies.
The Houthis have shown an ability to strike far beyond Yemen and disrupt shipping lanes around the Arabian Peninsula and the Red Sea - as they did in support of Hamas in the Gaza war - and could target the Bab el-Mandeb Strait off the coast of Yemen, a choke-point for sea traffic towards the Suez Canal.
With US midterm elections due in November, the increasingly unpopular war has weighed on Trump's Republican Party.
He has appeared eager to end it soon, while also threatening escalation.
Demonstrators took to city streets across the US on Saturday in anti-Trump rallies described by organisers as a call to action against the war on Iran.
Trump has threatened to hit Iranian power stations and other energy infrastructure if Iran does not open the Strait of Hormuz. But he extended a deadline he had imposed for this week, giving Iran another 10 days to respond.
Iranian threats to attack ships in the strait have kept most oil tankers from attempting the waterway.
Iran has agreed to allow an additional 20 Pakistani-flagged vessels to pass through the strait, with two ships permitted to transit daily, Pakistani Foreign Minister Ishaq Dar said.
