A German kidnapped by Somali pirates eight years ago may now be held captive by Islamic militants in the southern Philippines, the country's military said Monday after finding the man's yacht and a woman's body inside.

Regional military spokesman Maj. Filemon Tan said Abu Sayyaf spokesman Muamar Askali claimed the militants kidnapped Jurgen Gustav Kantner and killed his female companion while the couple were cruising off neighboring Malaysia's Sabah state.

It's not clear why the woman was purportedly killed, but it's possible she may have fought back or tried to escape, Tan and another military official said.

Villagers reported finding a dead woman lying beside a shotgun on board a light blue yacht with the German flag and marked "Rockall" off Laparan Island in Sulu province, Tan said. The southern province is where ransom-seeking militants have held many hostages in jungle camps.

Kantner, 69, and his wife were reportedly kidnapped off Somalia on board the Rockall in 2008 and later freed by Somali pirates, Tan said. Authorities did not know whether the woman kidnapped in Somalia is the same woman who was killed.

Troops took custody of the woman's body and the yacht Monday. Both were being examined by police investigators in Tawi Tawi province near Sulu, the military's Western Mindanao Command said in a statement.

"Alarming is that the body found was naked and had several contusions to the face and was possibly raped," the military said.

In Berlin, Foreign Ministry spokesman Martin Schaefer said German authorities were working with their Philippine counterparts to learn what happened.

"We can and will confirm such reports ... only when German consular employees have really established without doubt, with their own eyes and ears or by other means, that they are correct," Schaefer said. "We're not there yet."

The Abu Sayyaf, which is blacklisted by the U.S. and the Philippines as a terrorist organization, holds more than a dozen foreign and local hostages.

Abu Sayyaf and allied gunmen have committed many attacks at sea despite efforts by the Philippines, Malaysia and Indonesia to jointly shore up security along their busy sea border. Indonesians and Malaysians have been kidnapped from tugboats and fishing boats in recent months.

Indonesia's Foreign Ministry confirmed receiving information about the separate kidnappings of two Indonesian skippers of vessels off Sabah over the weekend, saying it was in touch with Malaysian and Philippine government officials about the latest abductions.

Indonesia's government has urged Indonesian crewmen in Sabah to avoid sailing in the risky waters until security has improved, the ministry said.

The kidnappings have continued despite one of the largest military offensives against Abu Sayyaf, mainly in Sulu and the nearby island province of Basilan, involving more than 6,000 troops, navy gunboats and rocket-firing air force aircraft.

Without a known foreign source of funds, Abu Sayyaf has survived mostly on ransom kidnappings, extortion and other acts of banditry.

A confidential Philippine government threat assessment report seen by The Associated Press said the militants pocketed at least 353 million pesos ($7.3 million) from ransom kidnappings in the first six months of the year and have turned to abductions of foreign tugboat crewmen as military offensives restricted their mobility.

Anticipating that the Abu Sayyaf may soon demand ransom for the German, Tan appealed for people to follow the Philippine government's no-ransom policy.

"If we give in to ransom, a greater damage will be done. They can use the money to buy arms and to feed their bandits and that will fuel again the tendency for them to kidnap," Tan said. "It becomes a lucrative business."

Philippine President Rodrigo Duterte, who took office June 30, has ordered troops to destroy the Abu Sayyaf and has ruled out the possibility of any peace talks with them. He has pursued talks with two other larger Muslim insurgent groups.

The government report said the Abu Sayyaf had 481 fighters with 438 firearms in the first half of the year, but the military reported last week that it had killed 70 of the militants and captured 32 others since July in Basilan and Sulu, a Muslim province about 950 kilometers (590 miles) south of Manila.

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AP writer Geir Moulson in Berlin contributed to this report.

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This story has been corrected to show the man allegedly kidnapped is Jurgen Gustav Kantner, not Juegen Kantner.