(CNN) -- Yemeni authorities working with the U.S. Navy intercepted a ship carrying a "substantial" cache of "illegal arms" such as surface-to-air missiles, potent explosives and rocket-propelled grenades, a U.S. official and Yemen's government said Monday.
The incident took place in Yemeni territorial waters in the Arabian Sea last Wednesday, according to a statement issued five days later from Yemen's embassy in Washington.
The crew of the USS Farragut, a Naval destroyer, was working with Yemeni authorities when they spotted the vessel, said an official in the Obama administration. The ship had several flags onboard, but no reliable documentation showing where it came from, the official added Monday.
After the ship was intercepted, Yemeni coast guard officers boarded it and "found a large cache of illegal arms," according to the Yemeni embassy's statement, which was also posted on the website of the Arabian country's state-run SABA news agency.
The firepower included anti-aircraft missiles, C4 military-grade explosive, ammunition and bomb-making equipment such as circuits, remote triggers and various handheld explosives, the Yemeni statement said.
There were eight Yemeni crew members aboard the vessel.
The Obama administration official described the effort as a joint operation, and said U.S. forces joined their Yemeni counterparts in boarding the suspect boat.
CNN's Barbara Starr reported this story from Washington, and Greg Botelho wrote it from Atlanta. CNN's Hamdi Alkhshali contributed to this report.