(CNN) -- Pirates boarded an American yacht off the coast of Oman three days after the boat's owners split off from the relative safety of a sailing group traversing a dangerous section of the Indian Ocean, according to the group, the Blue Water Rally.
The yacht, the S/V Quest, was overtaken by pirates on Friday, according to U.S. officials.
Owners Jean and Scott Adam and two other people on board, Phyllis Macay and Bob Riggle, had been traveling with yachts participating in the Blue Water Rally since their departure from Phuket, Thailand, the rally group said Sunday in a statement on its website. But they broke off on February 15 after leaving Mumbai, India, to take a different route, the group said.
"We feel desperately sorry for our four friends onboard and our thoughts are with them and their friends and family," the London-based group said in a posting on its website. "All the yachts still on the rally are fine and well."
U.S. officials have not identified the people on board the ship, but have confirmed that four U.S. citizens are involved.
U.S. officials have made no further comment on the situation since Rear Adm. Charles Gaouette, deputy commander of the U.S. Navy's Fifth Fleet, said Saturday that the government is evaluating its options.
Another U.S. official, who asked not to be named due to the sensitivity of the situation, said previously that the United States is determining what military assets are in the region and the capabilities of the personnel onboard. The official said that the pirates are believed to be onboard the yacht with the Americans, and the next step would be to determine whether the military could keep the yacht from reaching the shore -- either by blocking or harassing it.
The Adams are experienced boaters, having started a world tour in 2004, and were very much conscious of the threat from pirates, said a friend of the Adams, fellow boater Scott Stolnitz..
Scott Adam said several weeks ago that he was concerned about pirate activity in the area, which he had never visited before, Stolnitz said. But he said Adam was determined to traverse the world himself as opposed to shipping the boat -- as some other yacht owners have done.
Stolnitz also said the Adams had also been traveling with others on a "buddy boat," but those people decided not to continue.
On their website, the Adams say their mission "is to allow the power of the Word to transform lives ... (and) seek fertile ground for the word and homes for our Bibles."
But Stolnitz said vigorous evangelism wasn't a major emphasis for the couple.
"They use the Bible as an ice breaker," he said.
The couple posted to their website earlier this year about their travel plans, including a refueling stop in Djibouti, another pirate flash-point.
"Djibouti is a big refueling stop," said the post, which is not dated. "I have no idea what will happen in these ports, but perhaps we'll do some local touring."
They also sent out an e-mail several days ago expressing some unease, Stolnitz said.
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 sentenced to more than 30 years in prison.
CNN Pentagon Correspondent Barbara Starr and CNN's David McKenzie contributed to this report.