The US and Iran traded strikes on Tuesday, as concerns rose that the weeks-long lull in the war is at an end.
Iranian media reported several strikes near Bandar Abbas, on the Strait of Hormuz, early on Wednesday, and local officials said that another strike in Sirik killed at least four people, including a child, at a wedding.
Supreme leader Ayatollah Mojtaba Khamenei said Iran had "unforgettable lessons for the American enemy".
Earlier, US Central Command said its forces were striking targets belonging to Iran's Islamic Revolutionary Guard Corps.
It said the strikes followed recent attempted attacks by the IRGC against commercial shipping in the Strait of Hormuz and US service members posted in the region.
US President Donald Trump said that the "large and powerful" strikes were in retaliation for the "Iranians’ failed attempt at adding sea mines to the strait … and the Iranians shooting eight missiles, all successfully knocked down, at our military base in Jordan".
In a post on Truth Social, he warned that "if the failed nation of Iran retaliates for this very justified attack, they will be hit again at a much harder and higher level".
Mr Trump also warned of the "biggest attack of them all", which he said was "waiting in the wings and, when it is over, there will be very little left of the Islamic republic of Iran".
After the strikes, semi-official news agency Mehr said that the IRGC had launched a "regrettable response" to the US attacks.
The IRGC released footage it said shows ballistic missiles being launched toward US military positions in Jordan.
Centcom did not comment on the alleged strike at a wedding.
Before the alternating strikes began at the weekend, the US and Iran had been in an uneasy stalemate, with start-and-stop discussions taking place over the reopening of the Strait of Hormuz.
The US had instead been focusing its energies on wearing Iran down economically, with a new tranche of sanctions announced over the past several days, and more reportedly to come.
