By Barbara Starr and Greg Botelho

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.