American and Iranian ships were involved in an "unsafe" incident in the Persian Gulf, according to the US military.
Footage released by the US Navy from 2 April showed what it said was a ship, commanded by Iran's Islamic Revolutionary Guard Corps (IRGC), cutting in front of the USCGC Monomoy, causing the vessel to stop quickly.
The American vessel was conducting a "routine maritime security patrol in international waters" at the time of the incident, according to the Navy.
It is thought to be the first such incident for nearly year.
The IRGC also did the same with another American vessel, the USCGC Wrangell, said Commodore Rebecca Rebarich, a spokeswoman for the US Navy's Mideast-based 5th Fleet.
Iran did not immediately acknowledge the incident, which led to no injuries or damage to the vessels.
"The US crews issued multiple warnings via bridge-to-bridge radio, five short blasts from the ships' horns, and while the [Iranian] Harth 55 responded to the bridge-to-bridge radio queries, they continued the unsafe manoeuvres," Cdre Rebarich said.
"After approximately three hours of the US issuing warning and conducting defensive maneuvers, the [Iranian] vessels manoeuvre away from the US ships and opened distance between them."
Continuing, Cdre Rebarich said the interaction marked the first "unsafe and unprofessional" incident involving the Iranians since 15 April 2020.
While 2018 and 2019 remained largely free of such incidents, the Navy recorded 14 incidents in 2017, 35 in 2016, and 23 in 2015.
The incident comes as Iran negotiates with world powers to return to the deal that then-US President Donald Trump announced he was pulling out of it in 2018.