Investigators have not yet determined where the boat came from or where it was headed, but it was boarded in an area where the US Navy has previously confiscated Iranian-supplied arms destined for war-ravaged Yemen.

"We're not ready to pin this on anyone yet, we are doing an investigation of the evidence," the US official said.

The incident occurred Tuesday when sailors from the USS Jason Dunham boarded a small skiff that was having engine trouble and taking on water.

On board, they found about 600 bags filled with small arms -- mostly AK-47s -- totalling more than 1,000 rifles, the official said.

The skiff sailors were then transferred to the Yemeni coastguard. Their nationality was not released.

The official said it was the first time since 2016 that the Navy had made a small arms seizure like this.

Yemen's devastating conflict has left nearly 10,000 people dead since March 2015, when a Saudi-led coalition intervened to fight Iran-backed Huthi rebels closing in on the last bastion of President Abedrabbo Mansour Hadi's government.