The strikes reportedly occurred in the narrowest section of the Strait of Hormuz.
US fighter jets have struck Islamic Revolutionary Guard Corps (IRGC) speedboats as explosions were heard near the port of Bandar Abbas.
The attack occurred on Monday as US and Iranian negotiators arrived in Qatar in hopes of advancing stalled talks.
According to Iranian outlet SNN, the attack on the Iranian vessels took place south of Larak Island, in the narrowest section of the Strait of Hormuz, which remains under a dual US-Iranian blockade. At least three Iranian sailors were killed, SNN said.
Media outlets also reported a series of explosions in Bandar Abbas, home to an Iranian naval base.
Al Jazeera journalist Ali Hashem cited an Iranian official as saying that the IRGC targeted an unidentified vessel after US jets struck IRGC boats. The source added that gunfire was heard near Bandar Abbas.
The US Central Command (CENTCOM) later said in a statement that US forces had “conducted self-defense strikes in southern Iran today to protect our troops from threats posed by Iranian forces.” The statement added that the targets included missile sites and “Iranian boats attempting to emplace mines.”
Earlier, the US military had warned that it would intervene in response to Iranian attacks on ships transiting the strait.
Iran closed the vital shipping lane to vessels from “hostile countries” in response to the US and Israeli airstrikes launched on February 28. Last month, the US announced a blockade of Iranian ports.
The fragile truce reached between the US and Iran on April 8 has largely held, despite US President Donald Trump repeatedly threatening to resume the bombing campaign unless Tehran agrees to his demands.
“conducted self-defense strikes in southern Iran today to protect our troops from threats posed by Iranian forces”
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