MANILA - A Dutch taxidermist held by Muslim militants in the Philippines' volatile south since 2012 was killed on Friday (May 31) following a clash between his captors and government troops.

Mr Ewold Horn, 59, from Groningen, in the Netherlands, died while trying to flee during an early-morning gunbattle in the jungles of Sulu province's mountainous Patikul town, Brigadier-General Divino Pabayo Jr, head of Joint Task Force Sulu, said in a statement.

He said Mr Horn was shot at by men of Radullah Sahiron, head of a faction of the notorious, pro-Islamic State Abu Sayyaf group.

"We tried our very best to safely rescue him from his captors," said Brig-Gen Pabayo.

Six militants were killed in the firefight, including Sahiron's second wife, Mingayan Sahiron.

"He ran. He managed to get far. We found him dead on the ground alongside Sahiron's wife. She must've been running after him when they were both killed in a hail of gunfire," Colonel Gerry Besana, spokesman of the Western Mindanao Command, told reporters.

Security forces were pursuing militants who attacked a group of soldiers earlier in the week when they chanced upon the group holding Mr Horn.

Col Besana said Mr Horn was the last foreigner to be held hostage by the Abu Sayyaf

Mr Toshio Ito, a self-styled Japanese treasure hunter who is now in his mid-sixties, was kidnapped in 2010. But the militants were said to be no longer treating him as a hostage, but as one of their own.

Mr Horn was abducted with Swiss Lorenzo Vinciguerra, 53, a taxidermist for a museum in Switzerland, and their Filipino guide Ivan Sarenas, a wildlife photographer, during a bird-watching expedition in Tawi-Tawi, the Philippines' southernmost province, in February 2012.

They were at the time searching for the Sulu hornbill, considered the most endangered of the species in the world.

The three were heading back to the provincial capital of Bongao by boat after spending three days in a forest when they were waylaid and taken by five rifle-toting men.

Mr Sarenas managed to flee just hours later by diving into the water and swimming away, as the boat he was on was just about half-a-kilometre from the shore.

Mr Vinciguerra himself escaped two years later.

He recounted how he grabbed a machete from his guard, as government forces rained artillery rounds on the camp where he was being held.

In the scuffle, his cheek was sliced, but he managed to slit his guard's throat. He ran away, but was shot. Security forces later found him sprawled on the ground.

Mr Vinciguerra said he shouted at Mr Horn to flee with him, but that the Dutchman was "very sick and very weak".

Earlier this month (May), Sulu police commander Pablo Labra said he received unconfirmed reports that Mr Horn was already suffering from Stockholm syndrome, a condition that causes hostages to have feelings of trust or affection towards their captors.

"We received information that he has been spotted carrying a weapon… We really don't know if he has fought troops, but if he engages security forces and the lives of our troops are put in grave danger then we have no other recourse but to fight back," said Mr Labra.

This week's skirmishes between the military and extremists came five months after an Abu Sayyaf faction bombed a cathedral in Jolo, the capital of Sulu province, killing 23 people and wounding about 100.

President Rodrigo Duterte deployed additional forces in the region to search for the perpetrators of the church attack, for which officials blamed an Abu Sayyaf leader, Hatib Hajan Sawadjaan.

Mr Sawadjaan is believed to have replaced Isnilon Hapilon as the regional Islamic State emir after the latter was killed in 2017 during the government's successful effort to recapture the southern city of Marawi.

Though the group officially has a separatist, Islamist agenda, the Abu Sayyaf has capitalised on decades of instability in the war-torn southern island of Mindanao to generate tens of millions of dollars from piracy and ransom payments.

Since it turned kidnapping into a lucrative trade, the group has already beheaded an American, a Malaysian, two Canadians and a German.