The vessel, named the Quest, was being shadowed by the military after being captured by pirates off the coast of Oman on Friday. Officials had said earlier Tuesday it was less than two days from the Somali coast.
Americans Jean and Scott Adam -- the owners of the ship -- along with Phyllis Macay and Bob Riggle had been traveling with yachts participating in the Blue Water Rally since their departure from Phuket, Thailand, rally organizers said Sunday in a statement on the event's website. The group, which organizes long-distance group cruises, said the Quest broke off on February 15 after leaving Mumbai, India, to take a different route.
As negotiations were ongoing with the pirates for the hostages' release, gunfire was heard at about 1 a.m. ET Tuesday, U.S. Central Command said.
"As (U.S. forces) responded to the gunfire, reaching and boarding the Quest, the forces discovered all four hostages had been shot by their captors," the statement said. "Despite immediate steps to provide life-saving care, all four hostages ultimately died of their wounds."
The pirates engaged the U.S. forces on board, officials said. Two pirates were killed in the skirmish and 13 were captured and detained. Two others were already in U.S. forces custody, the statement said, and the remains of two pirates were found on board. "In total, it is believed 19 pirates were involved in the hijacking" of the vessel, Central Command said.
Forces had been monitoring the Quest for three days, officials said. Four U.S. Navy warships were involved in the response force -- an aircraft carrier, a guided-missile cruiser and two guided-missile destroyers, according to the statement.
A senior military official said on Monday the military was trailing the yacht. U.S. officials have not identified the people on board the ship, but confirmed that four U.S. citizens were involved.
Another U.S. official, who asked not to be named due to the sensitivity of the situation, had said previously that the United States was determining what military assets were in the region and the capabilities of the personnel on board.
They were very conscious of the threat posed by pirates, Stolnitz said, adding that Scott Adam had said weeks before that he was concerned about pirate activity in the area, a region he had never visited. But, he said, Adam was determined to sail the world himself rather than ship his boat, as some other yacht owners have done.
The Adams' website chronicles their worldwide voyage, which included trips to New Zealand, China, Cambodia and Panama.
One aspect of their travels, according to the site, "is friendship evangelism -- that is, finding homes for thousands of Bibles, which have been donated through grants and gifts, as we travel from place to place." They also say their mission is to "allow the power of the Word to transform lives."
But, Stolnitz said, vigorous evangelism wasn't a major emphasis for the couple. "They use the Bible as an ice breaker," he said.
Their travel plans for the Blue Water Rally included a refueling stop in Djibouti, according to the couple's website. "Djibouti is a big refueling stop," it said. "I have no idea what will happen in these ports, but perhaps we'll do some local touring."
However, Stolnitz said the couple had expressed some unease in an e-mail sent several days before the hijacking.
Piracy has flourished off the coast of Somalia, which has not had an effective government for two decades. In April 2009, pirates seized the U.S.-flagged Maersk Alabama, leading to a standoff in the Indian Ocean.
U.S. forces moved to rescue American Capt. Richard Phillips after seeing a pirate aiming a weapon on his back, officials said at the time.
Three pirates were killed and one was arrested. The Somali man arrested was convicted of acts related to high-seas piracy and was sentenced last week in New York to more than 30 years in prison by a federal court.
