MANILA (AFP) - Terrorists are planning to kidnap foreigners in tourist hotspots across the central and western Philippines, Western governments said on Wednesday (May 10) following a foiled abduction attempt by Islamic militants a month ago.

President Rodrigo Duterte said security had been increased on the western island of Palawan, one of the Philippines' most popular tourist destinations, after the US embassy warned of a kidnapping threat there.

"The US Embassy has received credible information that terrorist groups may be planning to conduct kidnapping operations targeting foreign nationals in the areas of Palawan," it said in a travel advisory.

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 400km north-west of the southern islands that are strongholds of the Abu Sayyaf, militants who have pledged allegiance to the Islamic State in Iraq and Syria (ISIS) militant 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 authorities became aware of the plot.

Security forces found the militants a day after they arrived on speedboats from Bohol, which is 500km north from the Abu Sayyaf's bases, 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 and the neighbouring island of Cebu, which has a major city of the same name.

The Abu Sayyaf has since its founding in the 1990s kidnapped dozens of foreigners and many more locals to extract ransoms.

KIDNAPPINGS FOR RANSOM

The militants typically raid coastal areas after sailing from their southern island strongholds on speedboats, although in recent years they have also attacked cargo and merchant ships.

They 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.

Still, in recent years the kidnapping threat had largely been restricted to the southern Philippine region of Mindanao.

Until recently, foreign governments had not warned of kidnapping threats in the central and western Philippines.

Fresh advisories from the Canadian and British embassies on Wednesday that backed up the American warning about Palawan also referred to tourist hotspots in the central Philippines near Bohol.

These included Dumaguete, Siquijor and Cebu.

Asked in Manila about the latest travel warnings for Palawan, Duterte said he wanted the suspects dead.

"My order to the security forces is shoot them on sight. Kill them," Duterte said.

Duterte last year ordered a major military offensive to extinguish the Abu Sayyaf on their southern bases, but the militant threat continued to grow.

The Philippines is looking to conduct joint patrols with Indonesia and Malaysia to stop the rising number of kidnapping raids on cargo and merchant vessels near the Abu Sayyaf's bases.

Duterte on Wednesday repeated a warning that the ISIS group was gaining influence in the Philippines.

"We have a problem with terrorism. What looms very big ahead is ISIS. They are coming in," Duterte said.

The Abu Sayyaf and other militant groups have in recent years pledged allegiance to ISIS.