In the contested Strait of Hormuz, where the renewed conflict has again cut off global energy supplies from the Middle East, US Marines boarded a tanker and another ship was reported to have been hit by a projectile.
The warring sides have been testing the limits of escalation since their ceasefire agreement collapsed, raising the prospect of a return to all-out war.
US President Donald Trump has threatened to launch broad-based air strikes on Iran's infrastructure, and has also declined to rule out a ground assault on Iran's coast or islands.
US officials have said attacks on southern Iran are designed in part to give Trump options.
But such moves risk provoking Iran to escalate in turn by hitting infrastructure of neighbouring countries, or further disrupt energy supplies by having its allies in Yemen attack shipping from the Red Sea.
The US military's Central Command included "military logistics infrastructure" in the list of targets it said it had struck in its latest attacks on Iran, the first time it has mentioned infrastructure in more than a week.
For now, the attacks appeared to be limited mainly to southern coastal areas that have already been targeted intensively in recent days.
Iranian state media said at least five bridges had been struck in the south.
Seven people were reported killed in attacks on bridges in the southern port of Bandar Khamir, where the train station was also hit.
An airport was reported hit further east and away from the coast in Iranshahr, in a province bordering Pakistan.
Other reported deadly attacks included one that killed a woman and wounded her child in the port of Bandar Abbas.
Iran said it had struck US bases in Kuwait and Bahrain, and a US radar station in Oman.
Explosions were also heard in the Qatari capital Doha, where the interior ministry said a child was wounded by shrapnel.
Iran said it fired at Syria, apparently for the first time in the war, targeting what it described as a US special forces base in Tanf.
Syria says US forces pulled out of the base there earlier in 2026, and a source said the strike caused no damage or casualties.
An interim agreement to end the war has collapsed since July 7, when Iran struck ships in the Strait of Hormuz and the United States responded with air strikes.
The renewed fighting has once again largely halted traffic through the world's most important energy shipping route, sending oil prices surging.
Iran has announced the closure of the strait, and Washington has reimposed its own blockade of Iranian ports.
In the latest incidents at sea, the US military said it had boarded the tanker Wen Yao to enforce the blockade.
The British maritime security service UKMTO reported a tanker had been hit by a projectile on Thursday off the coast of Oman.
While both sides have exchanged strikes daily, they have stopped short of escalating beyond parameters set earlier in the war, when civilian infrastructure and major economic targets were mostly deemed out of bounds because of the threat of retaliation.
Iran has vowed to attack civilian infrastructure across the Middle East if Trump follows through on threats to attack Iran's infrastructure.
The surge in energy prices generated by the conflict has created pressure on Trump to end the unpopular war as quickly as possible.
But leaving Iran in control of the strait would be a strategic embarrassment in a region where US forces have served as the main security guarantor for generations.
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