Foreign Minister Abbas Araqchi announced on social media that the strait, a slender chokepoint in global energy trade, was open for all commercial vessels for the remainder of the US-brokered 10-day truce that was agreed on Thursday between Israel and Lebanon.
US President Donald Trump told supporters at a rally in Arizona that Araqchi's announcement marked "a great and brilliant day."
But subsequent statements and clarifications from both sides left uncertainty over how quickly shipping might return to normal, and some vessels could be observed making unsuccessful attempts cross the strait on Friday before turning back.
Trump said a US blockade of ships sailing to Iranian ports, announced after talks with Iran last weekend ended without agreement, would remain until "our transaction with Iran is 100% complete".
Iran responded sharply, with Iran's parliament speaker and senior negotiator Mohammad Baqer Qalibaf saying in a social media post that the strait, which until recently carried about a fifth of the world's oil trade, "will not remain open" if the US blockade continues.
Oil prices settled down by around 9% on Friday after Iran said passage for all commercial vessels through the Strait of Hormuz.
