Iran has closed the Strait of Hormuz to vessel traffic, citing alleged violations of a ceasefire agreement by the US and Israel.
Tehran's top joint military command, Khatam al-Anbiya Central Headquarters, confirmed the move was the "first step" in response to what it described as breaches of commitments.
Officials warned that further measures would be taken if "aggression" continued.
Reports from Tehran emerged as Vice President JD Vance told Fox News he was confident the ceasefire agreed to in Washington's 14-point deal with Tehran would hold and that he saw no evidence the crucial waterway was closed.
The Islamic Revolutionary Guard Corps (IRGC) has warned vessels not to approach the Strait, adding their security would otherwise be at risk.
A spokesman from the IRGC Navy cited Israeli actions in Lebanon plus an alleged US violation of ceasefire commitments for closing the Strait.
It comes as Vice President Vance said he expects to travel to Switzerland for talks with Iran soon.
He said: "I expect that I will leave sometime in the next couple of days, but you know it's always a delicate coordination dance and the diplomatic protocols."
The Strait has reportedly been closed yet again
|REUTERS
A spokesman for the Israel Defense Forces (IDF) said that it "remains committed" to the ceasefire agreement brokered with the Iran-backed Hezbollah in Lebanon.
In a statement, the spokesman added the group will "continue to operate to remove any threat posed to the State of Israel and IDF soldiers".
Just hours earlier, Israeli strikes in Lebanon killed at least 16 people on Saturday, Lebanese Civil Defences said, hours after a ceasefire with Hezbollah took effect.
Lebanese media said Israeli warplanes and drones had hit multiple locations in the south and the Bekaa Valley, with Israel saying it was responding to projectiles fired by the Iran-backed group.
LATEST DEVELOPMENTS FROM IRAN
The site of an Israeli air strike on a house as rescuers try to recover bodies from under the rubble
|REUTERS
Hezbollah also said it remained committed to the ceasefire but would respond to any attempt by Israel to "seize territory or expand its occupation".
The group said Israeli forces attempted overnight to infiltrate the Ali al-Taher hill area in southern Lebanon.
It said its fighters engaged them, after which Israel carried out airstrikes inside and outside its declared operational area.
A senior Hezbollah official said the group would not allow Israel "freedom of movement" in Lebanese territory, adding that resistance remained legitimate while Israeli forces remained in Lebanon.
Rescuers embrace as they work at the site of an Israeli air strike in Barish
|REUTERS
One of the deadliest Israeli strikes hit a three-storey residential building in the southern town of Barish in the Tyre district, killing a father, a mother and their two children, a town official said.
The Lebanese army said an Israeli strike had killed a soldier on the Kfarrumman-Nabatieh road.
Israel's Arabic-language military spokeswoman said calm could be achieved if Hezbollah halted what she described as hostile activity and violations of agreements.
She said Israel's presence in a security zone aimed to remove threats and dismantle Hezbollah infrastructure, not harm civilians.