The four Americans aboard their captured yacht, S/V Quest in the Indian Ocean, have been shot dead by Somali pirates, the US military has reported.
US naval forces on the way to try to rescue the Americans heard gunshots and on arrival found the four hostages had been killed.
Two pirates were killed and 15 detained during the incident..
The remains of two other pirates, who had been dead for some time, were found. The US military did not state how those two died. In total the US said 19 pirates were involved in the hijacking of the yacht.
The deaths of Jean and Scott Adam, Phyllis Macay and Bob Riggle mark the first time US citizens have been killed in Somali pirate attacks.