A truce reached in June has descended into daily attacks and counterattacks, largely halted shipping traffic in the vital Strait of Hormuz and sparked fresh investor concerns about the repercussions for the global economy of the war the US and Israel launched in February.
The US military said it completed another night of strikes on Iran "to further degrade Iranian military capabilities", including on Qeshm Island and near Bandar Abbas, home to Iran's largest port, as well as key naval and Revolutionary Guards facilities.
"US forces, including fighter jets, aerial drones, and warships, launched precision munitions that hit dozens of Iranian military targets such as coastal surveillance and air defence sites, military logistics infrastructure, and maritime capabilities," the US Central Command said on Thursday.
A civilian was killed in a US strike on the Pasabandar area near the southeastern port city of Chabahar, Iran's semi-official Tasnim news agency said.
Iran has fired missiles and drones at US military bases in neighbouring states, including an air base in Jordan.
Early on Friday, Iran's military said it had attacked US facilities in Bahrain and Kuwait.
Iranian media reported that five bridges were hit in the latest round of US strikes, as well as the train station in coastal Bandar Khamir and Iranshahr Airport in southeastern Iran.
Seven people were killed in US attacks on bridges in Bandar Khamir, a port city in southern Iran, state news agency IRNA reported.
Iran's state media said the Revolutionary Guards had attacked a US special operations command centre in al-Tanf, Syria, in retaliation for the killing of Iranian soldiers in Iranshahr.
This marks the first direct attack by Iran on Syria, which has sought to avoid being drawn into a conflict that has engulfed neighbouring countries.
Iran's Revolutionary Guards said they had targeted and destroyed a naval radar system on the Salameh Rocks and a US air control radar in Oman's Ghannem area, Iranian state media reported.
The escalation in attacks has once again largely halted traffic through the Strait of Hormuz, the world's most important shipping route for oil and gas, pushing up oil prices and raising fresh concerns about the knock-on effect on inflation.
Tehran resumed its blockade of the strait, and Washington has again blockaded Iranian ports since Wednesday.
Iran last week hit ships moving through a corridor in the strait.
White House press secretary Karoline Leavitt told a briefing on Thursday that President Donald Trump would not "sit by and allow these active acts of terrorism to take place in the strait without ensuring Iran pays consequences for that".
But she said the president was "always open to diplomacy at the very same time".
Iranian sources said Iran's aim was to establish its authority over the strait, although Tehran was not keen on an escalation that would torpedo June's memorandum of understanding, which it still regards as giving it most of what it sought.
Iran wants all ships to travel through a channel close to its shores and intends to charge passage fees at the end of a 60-day negotiation period set in the memorandum.
Washington had encouraged ships to use an alternative route to the south, along the Omani coast.
US forces said their air strikes have hit military targets along the coast to cripple Iran's ability to control the strait.
Iranian Army spokesman Brigadier General Mohammad Akraminia said this would not work because Iran could strike the strait from anywhere on its territory.
Trump has repeatedly threatened to hit Iranian power plants and bridges next week unless Tehran resumes negotiations.
