Soldiers place the body of Ewold Horn into a body bag after he was killed by his captors in Philippines on Friday. Reuters

Manolo B. Jara / Reuters

A Dutch photographer held hostage by Daesh-linked militants in the Philippines since 2012 was killed on Friday by his captors when he tried to escape during a firefight on a remote southern island, the military said.

Ewold Horn, a wildlife photographer, was shot by his guards from the Abu Sayyaf group when he tried to flee during a clash between government troops and the militants, said Brigadier General Divino Rey Pabayo, commander of a Joint Task Force on Sulu island.

Colonel Gerry Besana, the spokesman of the military's Western Mindanao Command, not only confirmed the death of Horn but also that of the wife of Abu Sayyaf top leader Rahulah Sahiron, identified as Mingayan Sahiron, in the clash.

Besana added this was on top of the killing of the five terrorists as well as the wounding of eight soldiers who figured in the one-hour clash on Friday morning in a 'barangay" (village) in the town of Patikul, Sulu, punctuated by heavy exchange of gunfire.

A terrorist shot and killed Horn when he reportedly tried to escape at the height of the encounter with about 30 heavily-armed Abu Sayyaf men while the soldiers were conducting blocking operations in the village, according to Besana.

Horn and a fellow photographer, Lorenzo Vinciguerra from Switzerland, were taken captive as they were sailing off an island called Tawi Tawi on a bird-watching trip more than seven years ago and later taken to Sulu. Vinciguerra escaped in 2014.

Dutch Foreign Minister Stef Blok said the Netherlands had informed Horn's family.

"I am shocked by this terrible outcome," Blok said, "I have been in contact with the family. I will ask my counterpart in the Philippines for further clarification."

Six militants were also killed in the firefight in the town of town of Patikul on Sulu, Pabayo said. The circumstances of the firefight were not immediately clear.

Philippine President Rodrigo Duterte condemned Horn's killing and sent condolences to his family.

"We vow to pursue his killers to the ends of the earth until they are brought to justice," the president's spokesman, Salvador Panelo, said in a statement.

Also killed during the clash on Friday was Mingayan Sahiron, the wife of Radullan Sahiron, a senior leader of the Abu Sayyaf, the military said.

Radullan Sahiron is on a US State Department wanted list with a $1 million reward for his capture since his involvement in the kidnapping of US tourists in 2001.

He was believed to have escaped the clash, another military spokesman said.