"The ASG (Abu Sayyaf group) is claiming to have kidnapped German National Juegen Kantner but the military needs to verify that," Western Mindanao Command spokesman Maj. Filemon Tan Jr. told CNN.
Abu Sayyaf spokesman Abu Rami made the claim, saying Kantner had been kidnapped in waters off Malaysia's Sabah state, Tan said. Tan said he had heard a voice recording in which Kantner, 70, appeared to be asking about his female companion, believed to be Sabina Wetch.
On Sunday, residents of Laparan Island in the Mindanao island group discovered the body of a female foreigner believed to be aged in her fifties on a yacht bearing a German flag and the name "Rock all (sic)," Western Mindanao Command said on its Facebook page. Accompanying images show the name as "Rockall."
The command is investigating whether the body is Wetch's.
"We are 95% sure the features of the deceased woman matched the photo on a passport, also recovered from the boat," Tan told CNN. He said the body had gunshot wounds and bruising to the face. "The woman was in pretty bad shape," he said.
Commenting on reports that Kantner and Wetch had been kidnapped and later freed by Somali pirates in 2008, Tan said he believed that to be the case, referencing another sailor's blog.
Abu Sayyaf's aims
Abu Sayyaf is headquartered in the restive Muslim-majority province of Mindanao in the country's far south. The violent extremist group
split from established Philippines separatist movement Moro National Liberation Front in 1991.
The Philippines is a predominantly Catholic country, but the south has historically had a large Muslim population. Abu Sayyaf's stated aim is to establish an independent Islamic state on the southern island of Mindanao.
The group first became active in the early 1990s and was responsible for bombings across the southern Philippines and in the Malaysian state of Sabah.
Following the 2001 terrorist attacks on the United States, Washington worked hard with the Philippine military to stop the group's activities.
Largely weakened by these attacks, Abu Sayyaf started to move from large-scale bombings to kidnappings.
Rise in kidnapping
The seas around the Philippines are the most pirated in the world, according to data producer IHS Markit.
Armed cells affiliated with Abu Sayyaf are suspected to have been behind at least six known cases of kidnap-for-ransom in waters off Sabah and the Southern Philippines between March and July, it said in a statement Sunday.
"The group has carried out kidnap-for-ransom operations in the past, but these were mostly from locations ashore," naval analyst Ridzwan Rahmat said.
"This latest spate of attacks at sea, taking place also within a relatively short time period, represents an escalation compared to what previously were isolated incidents," Rahmat said.
At the time, Tan told CNN Philippines Kjartan Sekikngstad's release was an offshoot of ongoing military operations against the Abu Sayyaf group.
The Moro National Liberation Front assisted authorities in the operation, he said.
Sekkingstad was abducted from a resort on Samal Island, in September 2015, alongside two Canadians and a Filipino woman, who was released.
Abu Sayyaf initially demanded a $6.3 million ransom for each of the victims to be paid by April 25, according to Philippine state media, one Canadian was killed after that deadline expired and the second after a subsequent June deadline. The Filipino woman was released in June.
It is unclear whether a ransom was paid to secure Sekkingstad's release.