US Secretary of State Marco Rubio characterised the effort to escort stranded tankers through the strait as defensive in nature, one day after the US military said it had destroyed several Iranian small boats, as well as cruise missiles and drones.
"There's no shooting unless we're shot at first," Rubio told reporters at the White House on Tuesday.
Asked what Iran would need to do to violate the ceasefire, US President Donald Trump said: "They know what not to do".
The Strait of Hormuz has been virtually shut since the United States and Israel began attacks on Iran on February 28, triggering disruptions that have pushed up commodity prices around the world.
Iran had effectively sealed off the strait, which handles one-fifth of the world's oil and gas supply, by threatening to deploy mines, drones, missiles and fast-attack craft.
The US has countered by blockading Iranian ports and mounting escorted transits for commercial vessels.
US Defense Secretary Pete Hegseth said the US had successfully secured a path through the waterway and hundreds of commercial ships were lining up to pass through. The four-week-old truce with Iran was not over, he added.
"Right now the ceasefire certainly holds, but we're going to be watching very, very closely," he said.
General Dan Caine, chairman of the US Joint Chiefs of Staff, said Iranian attacks against US forces fell "below the threshold of restarting major combat operations at this point".
Shortly after Hegseth spoke, the UAE's defence ministry said its air defences were again dealing with missile and drone attacks coming from Iran, though Iran's joint military command denied carrying out attacks.
The UAE's foreign ministry said in a statement that the attacks were a serious escalation and posed a direct threat to the country's security, adding that the Gulf Arab state reserved its "full and legitimate right" to respond.
After issuing a new map of the narrow strait with an expanded Iranian area of control, Iran's Revolutionary Guards warned vessels to stick to the corridors it had set or face a "decisive response".
The US military said on Monday that two US merchant ships made it through the strait, without saying when, while shipping company Maersk said the Alliance Fairfax, a US-flagged ship, exited the Gulf under US military escort on Monday.
Iran denied any crossings had taken place.
The war has killed thousands as it spread beyond Iran to Lebanon and the Gulf, and has roiled the global economy. The head of the International Monetary Fund said even if the conflict ended immediately, it would take three to four months to deal with the consequences.
Rubio said 10 civilian sailors were among those who had died in the ongoing conflict, adding that crew on vessels stranded in the waterway were "starving" and "isolated".
Trump told reporters in the Oval Office that Iran's military had been reduced to firing "peashooters" and Tehran wanted peace, despite public sabre-rattling.
"They play games, but let me just tell you, they want to make a deal," Trump said.
US and Iranian officials have held one round of face-to-face peace talks, but attempts to set up further meetings have failed.
Iranian Foreign Minister Abbas Araqchi said peace talks were still progressing with Pakistan's mediation. He was travelling to Beijing on Tuesday for talks with his Chinese counterpart, his ministry said. Trump is also due to visit China this month.
with AP
