Awwal 16, 1432 H/Feb 19, 2011, SPA -- Pirates have seized a yacht and its four American occupants in the Indian Ocean off the coast of Oman, piracy watchdog ECOTERRA International said Saturday. The yacht, the S/V Quest, belongs to American couple Jean and Scott Adam, who embarked on a round-the-world trip in 2004. It was not certain they were onboard. The possible identity of the other two American nationals was unknown. "If the owners are on board, it would be a sad log for the couple on their 7-year world journey," dpa quoted ECOTERRA International as saying. US navy officials confirmed they were aware of the hijacking by Somali pirates, which occurred Friday, and said they monitoring the situation. According to a website chronicling the Adams' voyage, they are travelling the world. Pirates range far from Somalia in their search for vessels to hijack for ransom, defying a fleet of international warships sent to curb the ever-growing threat. For the most part, ship owners give in to the multimillion-dollar ransom demands.