ABOARD THE USS JASON DUNHAM, Persian Gulf (AP) — U.N. investigators have boarded a U.S. military ship in an effort to determine if more than 2,500 assault rifles seized by the American ship off the coast of Yemen came from Iran.

The U.S. Navy says the weapons confiscated by the guided-missile destroyer USS Jason Dunham in late August were likely headed from Somalia to Yemen. But it's unclear where the AK-47s were manufactured and put on the smuggling route.

The cache is one of a handful of weapons seizures by the Navy in recent years, and underscores the challenge of tracking down smugglers in the waters around Yemen.

A few reporters were allowed to see the huge pile of rifles that were stacked in a corner on the Dunham and were already rusting from two months at sea.