Terrorists are planning to kidnap foreigners on a Philippine island popular with tourists, the US embassy has warned, a month after a foiled abduction attempt by Islamic militants at another tourism hotspot.
An advisory from the US embassy in Manila on Tuesday warned Americans to "carefully consider" going to Palawan, naming a World Heritage-listed underground river as one area of specific concern.
"The U.S. Embassy has received credible information that terrorist groups may be planning to conduct kidnapping operations targeting foreign nationals in the areas of Palawan," the advisory said.
The Philippine military on Wednesday said in a statement it "shared the same concerns" as the US government, and that it had increased security at Palawan's tourism sites.
The embassy identified two locations -- the capital city of Puerto Princesa and the nearby underground river that attracts thousands of visitors daily -- as areas the kidnappers were targeting.
Puerto Princesa is about 400 kilometres (240 miles) northwest of southern islands that are strongholds of the Abu Sayyaf, militants who have pledged allegiance to the Islamic State group and frequently kidnap foreigners.
The Abu Sayyaf last month attempted a kidnapping raid on Bohol island, a popular tourist destination in the central Philippines, but were foiled after security forces became aware of the plot.
Security forces found the militants a day after they arrived on Bohol on speedboats, and engaged them in a gun battle.
Nine militants, three soldiers and one policeman were killed in the clashes, according to authorities. They said another militant died in police custody.
The Bohol raid occurred days after the US embassy issued a warning of potential kidnappings there.
The Abu Sayyaf has since its founding in the 1990s kidnapped dozens of foreigners and many more locals to extract ransoms.
It typically raids coastal areas after sailing from its southern island strongholds on speedboats, although in recent years it has also attacked cargo and merchant ships.
The militants beheaded two Canadians last year and an elderly German sailor in February after demands for millions of dollars were unmet.
The Abu Sayyaf raided a resort in Puerto Princesa's Honda Bay in 2001, abducting three Americans and 17 Filipinos.
One of the Americans was beheaded, while one was killed in a military rescue attempt a year later. The third American was freed in the rescue effort.
The Abu Sayyaf has also kidnapped people from Malaysian coastal resorts, which are a short speedboat ride from its southern Philippine bases.