The US Navy said the ship was intercepted on January 6, carrying 2,116 AK-47 assault rifles.
The fishing vessel was passing through international waters en route from Iran to Yemen.
The crew included six Yemeni citizens.
Work is underway to return the crew to their homeland.
The US Navy also called the incident "a continuation of Iran's destabilizing activities."
In September, the United States reported an incident involving the Iranian side seizing military drones in the Red Sea.