Gerfa Yeatts Lunsmann was dropped off by boat late Sunday at a wharf and walked to nearby Maluso township on southern Basilan Island, where a patrolling police team picked her up, said military spokesman Lt. Col. Randolph Cabangbang. She was handed over to FBI agents in the Philippines.
Suspected Abu Sayyaf militants snatched the three on July 12 while they were vacationing with their relatives on an island near southern Zamboanga city. In a July 17 cellphone call to the captives' relatives in Virginia that was traced to Basilan, the hostage-takers demanded a huge ransom, according to Philippine officials.
It was not clear if any ransom was paid but that has been the case in previous abductions.
"We thank God for this release," Zamboanga Mayor Celso Lobregat told The Associated Press, adding that Lunsmann was "a bit weak."
The U.S. Embassy said in a statement Lunsmann's release "could not have occurred without the concerted efforts of Philippine government officials" and Lobregat's personal engagement.
Ransom kidnappings have long been a problem in the impoverished region and are blamed mostly on the al-Qaida-linked Abu Sayyaf, a group also notorious for beheadings and bombings. It was founded on Basilan in the 1990s as an offshoot of a violent Muslim insurgency that has been raging for decades.
U.S.-backed offensives have weakened the group, which is blacklisted by Washington as a terrorist organization, but it remains a key security threat. Hundreds of U.S. troops are stationed in the southern Philippines, including Basilan, to train and equip Philippine forces but are prohibited from engaging in military operations.
The Abu Sayyaf still holds an Indian, a Malaysian and a Japanese convert to Islam.
Lunsmann, a 41-year-old veterinarian who lives in Virginia, was born to a Muslim family near Zamboanga. She was adopted by an American couple as a child and grew up in the United States. She has visited her Philippine home province at least five times before, police said.
Associated Press writer Hrvoje Hranjski contributed to this report.