The yacht Quest was hijacked on Friday off the coast of Oman, but is now in the waters between Yemen and northern Somalia, two pirates and a Somali government official told The Associated Press.
One pirate who gave his name only as Hassan said a warship with a helicopter on its deck is near the Quest.
The pirate's claim could not be independently verified, and U.S. officials on Sunday did not release any information about the yacht. A U.S. Embassy spokesman on Saturday said officials were assessing options and "possible responses."
Hassan told the AP he is speaking directly with the pirates aboard the hijacked yacht. A second pirate who gave his name as Bile Hussein and a Somali official in Puntland who asked not to be named both said the Quest is in between Yemen and Somalia and heading closer to Puntland, a haven for pirates on Somalia's northern tip.
In New York, the first secretary of Somalia's U.N. Mission, Omar Jamal, said he had received reports from Somalia that the boat was expected to make landfall late Sunday.
Pirates have increased attacks on ships off the coast of East Africa, but Americans have rarely been targeted. The last attack against a U.S. crew - in 2009 - ended with Navy sharpshooters killing two pirates and rescuing the ship's captain.
If the Quest reaches Somalia's shores the four American hostages would likely be taken inland, where a fast resolution is much less likely. A British sailing couple who were released in November spent 388 days in pirate captivity.
The organizers of an international yacht race called the Blue Water Rally said the Quest had been taking part in the race but left it Feb. 15 to chart an independent course from India to Oman.
The Quest is owned by Scott and Jean Adam, a couple from California. The Blue Water organizers also identified the other two Americans onboard as Phyllis Mackay and Bob Riggle. The NBC TV station in Seattle, Washington spelled the name as Phyllis Macay and said she and Riggle are from Seattle.
"We feel desperately sorry for our four friends onboard and our thoughts are with them and their friends and family. All the yachts still on the rally are fine and well," the Blue Water website said.
The Adams have been sailing the world with a yacht full of Bibles since 2004. The hijacking of their yacht came two days after a Somali pirate was sentenced to 33 years in prison by a New York court for the 2009 hijacking of the Maersk Alabama. That case ended when Navy sharpshooters killed two pirates holding the ship's captain.
Pirates have increased attacks off the coast of East Africa in recent years despite an international flotilla of warships dedicated to protecting vessels and stopping the pirate assaults. Multimillion dollar ransoms are fueling the trade, and the prices for releasing a ship and hostages have risen sharply.
Pirates currently hold 30 ships and more than 660 hostages, not counting the attack against the Quest.
The best-known case of Westerners being held hostage in Somalia was that of Paul and Rachel Chandler, a British couple held for 388 days. The two, who were captured while sailing in their private yacht, were released in November.
The Adams - who are members of the Marina del Rey Yacht Club in Marina del Rey, California - run a Bible ministry, according to their website, and have been distributing Bibles to schools and churches in remote villages in areas including the Fiji Islands, Alaska, New Zealand, Central America and French Polynesia.
The pirates from Puntland in northern Somalia are not hardline Islamists and the fact the Adams carry Bibles is not likely to be a problem. Pirates in Puntland are known to spend their ransom spoils on alcohol, drugs and prostitutes.
Straziuso reported from Nairobi, Kenya.