The US Navy seized thousands of firearms including AK-47s from a boat in the Gulf of Aden on August 28, according to a defense official.
After counting, it was found that 2,521 AK-47 automatic rifles were seized.
The vessel, which was unflagged, was described as a dhow, a small sailboat that is common to the region. The official added that the number of weapons seized could exceed 1,000.
The boarding was carried out by the crew of the Arleigh Burke-class destroyer USS Jason Dunham, which was participating in a US Naval Forces Central Command operation.
The dhow’s crew allowed the US Navy to board upon its request.
The official said the boarded vessel’s destination was not immediately clear, though US officials have said that ships intercepted in this area in the past have been linked to Iranian efforts to support Houthi rebels in Yemen.
The US is analyzing the evidence on board to determine the boat’s origin and destination, the official said.
The US supports the Saudi-led coalition in its fight against the Iranian-backed Houthis, a conflict that has come under increased scrutiny amid concerns over civilian casualties.
The Gulf of Aden, which connects the Indian Ocean to the Red Sea, sees heavy maritime traffic and is frequently used by smugglers to move a variety of cargo.
US and allied warships participating in the Combined Task Force 150 have previously intercepted other ships in the area. In April, a French frigate seized thousands of pounds of illicit drugs worth millions of dollars.