Iran said it launched strikes against eight United States targets in Bahrain and Kuwait early Sunday morning local time.
It is the latest barrage in a flare-up of hostilities that began on Thursday and has threatened to undermine talks to end the Iran war.
Tehran said the strikes on military installations were in retaliation for attacks launched by Washington on multiple targets in Iran.
US Central Command said its airstrikes had been in response to what it said was an Iranian attack earlier on an oil tanker in the Strait of Hormuz.
The ship, the Panamanian-flagged tanker Kiku, carried crude oil for the state-run energy company of Qatar, a key negotiator between Tehran and Washington.
