The Gambia-flagged cargo ship Lian Star ignored more than 20 warnings from US forces overnight as it tried to enter an Iranian port, the military said.
The ship remained adrift in the Gulf of Oman and US forces have not boarded it, a US official with knowledge of the situation said.
With the latest action, the US military has stopped six ships trying to breach the blockade.
One was allowed to proceed.
Another 116 ships have been redirected, the military said.
The US launched the blockade on April 17 in response to Iran largely closing the strait after the war began with US and Israeli strikes on February 28.
A fragile ceasefire has held since April 7.
Now the region and wider world await word on whether a deal is being reached to extend it by 60 days while new talks would be held on Iran's disputed nuclear program.
Events in the Strait of Hormuz between Iran and Oman have shaken the global economy, with shipments of significant amounts of oil, natural gas and related supplies like fertiliser largely stranded, increasing the strain on consumers and food producers.
The US blockade seeks to limit Iran's own shipments and further weaken its access to funds, creating more pain for its long-weakened economy.
US President Donald Trump met with advisers on Friday but has yet to decide on whether to move ahead with a deal to extend the ceasefire and reopen the strait.
Iranian authorities have said the deal has not been finalised.
Commercial traffic has quietly continued to flow through the strait despite Iran's assertions that it must approve any transits, although at a much lower volume than before the conflict.
"Any violation of these regulations will place the security of their passage at serious risk," Iran's joint military command said on Saturday in a statement carried by state TV, warning that any military vessels trying to interfere with that would be targeted.
Iran has even charged tolls for transit as high as $US2 million ($A2.8 million), which experts have called a violation of a principle of international maritime trade: freedom of peaceful navigation.
Qatar's deputy prime minister, Sheikh Saoud bin Abdulrahman bin Hassan bin Ali Al Thani, on Saturday said his country opposes charging fees to transit, "but for certain times when they say they are going to use it for mine clearing or some usage of the fees for a temporary time, this is something that is negotiable, and it could be something that will help the transit of the Strait of Hormuz to be back to normal stage".
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