Philippine marines aboard an Amored Personnel Carrier (APC) and a truck guard a highway in Indanan town, Sulu province on the southern island of Mindanao on February 27, 2017, after reports of the beheading of German national Jurgen Kantner by the Abu Sayyaf group. - Islamic militants in the Philippines have beheaded the German hostage they were holding for ransom, the government in Manila said February 27. (Photo by NICKEE BUTLANGAN / AFP)
Philippine soldiers, wounded in an ongoing clash with Islamist militants from the Abu Sayyaf group, arrive at a military hospital in Jolo, Sulu province, on the southern island of Mindanao on March 3, 2017, hours prior to the arrival of President Rodrigo Duterte. - Philippine soldiers clashed anew on March 3 with Islamist militants behind the beheading of a German hostage. The Abu Sayyaf, a kidnap-for-ransom network in the southern Philippines that has declared allegiance to the Islamic State group, killed Jurgen Kantner, 70, on February 26 after its demands for 30 million pesos ($600,000) were not met. (Photo by NICKEE BUTLANGAN / AFP)
Filipino soldiers collect confiscated firearms from killed Abu Sayyaf members in the Philippine town of Ibanga on April 12, 2017.
Abu Sayyaf spokesman Abu Sabaya, right foreground, is seen with his band of armed extremists. Philippine troops captured an Abu Sayyaf rebel commander blamed for years of ransom kidnappings. AP Photo
Philippine soldiers walk along a highway as they return to camp after an armed encouter with members of militant group Abu Sayyaf at the village of Bongkaong, Patikul town, Sulu province on the southern island of Mindanao on August 26, 2016. - Philippine security officials killed six members of militant group Abu Sayyaf on August 26 including one involved in the kidnapping of two Canadians who were beheaded in the troubled south, the military said. (Photo by STRINGER / AFP)
This photo taken on September 5, 2016, Philippine soldiers standing guard next to an Armored Personnel Carrier (APC), inside a military camp in Jolo, Sulu province, in southern island of Mindanao, as they prepare for an operation against the extremist Abu Sayyaf group. - Philippine President Rodrigo Duterte has vowed to cannibalise and "devour" Abu Sayyaf Islamist militants who allegedly bombed his home city last weekend, killing at least 14 people and leaving dozens injured. (Photo by MARK NAVALES / AFP)
In this photo taken on August 30, 2016, Philippine soldiers firing howitzer cannons into Muslim extremist group Abu sayyaf's position in Jolo, Sulu province, in southern island of Mindanao, as troops carried out President Rodrigo Duterte's orders to "destroy" the militants. - Duterte tagged on September 3, the Abu Sayyaf, an Islamic militant group from the southern Philippines notorious for kidnappings, as a possible suspect in a deadly blast in his home town of Davao. (Photo by MARK NAVALES / AFP)
Philippine marines aboard an Amored Personnel Carrier (APC) and a truck guard a highway in Indanan town, Sulu province on the southern island of Mindanao on February 27, 2017, after reports of the beheading of German national Jurgen Kantner by the Abu Sayyaf group. - Islamic militants in the Philippines have beheaded the German hostage they were holding for ransom, the government in Manila said February 27. (Photo by NICKEE BUTLANGAN / AFP)
Philippine soldiers, wounded in an ongoing clash with Islamist militants from the Abu Sayyaf group, arrive at a military hospital in Jolo, Sulu province, on the southern island of Mindanao on March 3, 2017, hours prior to the arrival of President Rodrigo Duterte. - Philippine soldiers clashed anew on March 3 with Islamist militants behind the beheading of a German hostage. The Abu Sayyaf, a kidnap-for-ransom network in the southern Philippines that has declared allegiance to the Islamic State group, killed Jurgen Kantner, 70, on February 26 after its demands for 30 million pesos ($600,000) were not met. (Photo by NICKEE BUTLANGAN / AFP)
Filipino soldiers collect confiscated firearms from killed Abu Sayyaf members in the Philippine town of Ibanga on April 12, 2017.
Abu Sayyaf spokesman Abu Sabaya, right foreground, is seen with his band of armed extremists. Philippine troops captured an Abu Sayyaf rebel commander blamed for years of ransom kidnappings. AP Photo
Philippine soldiers walk along a highway as they return to camp after an armed encouter with members of militant group Abu Sayyaf at the village of Bongkaong, Patikul town, Sulu province on the southern island of Mindanao on August 26, 2016. - Philippine security officials killed six members of militant group Abu Sayyaf on August 26 including one involved in the kidnapping of two Canadians who were beheaded in the troubled south, the military said. (Photo by STRINGER / AFP)
This photo taken on September 5, 2016, Philippine soldiers standing guard next to an Armored Personnel Carrier (APC), inside a military camp in Jolo, Sulu province, in southern island of Mindanao, as they prepare for an operation against the extremist Abu Sayyaf group. - Philippine President Rodrigo Duterte has vowed to cannibalise and "devour" Abu Sayyaf Islamist militants who allegedly bombed his home city last weekend, killing at least 14 people and leaving dozens injured. (Photo by MARK NAVALES / AFP)
In this photo taken on August 30, 2016, Philippine soldiers firing howitzer cannons into Muslim extremist group Abu sayyaf's position in Jolo, Sulu province, in southern island of Mindanao, as troops carried out President Rodrigo Duterte's orders to "destroy" the militants. - Duterte tagged on September 3, the Abu Sayyaf, an Islamic militant group from the southern Philippines notorious for kidnappings, as a possible suspect in a deadly blast in his home town of Davao. (Photo by MARK NAVALES / AFP)
Philippine marines aboard an Amored Personnel Carrier (APC) and a truck guard a highway in Indanan town, Sulu province on the southern island of Mindanao on February 27, 2017, after reports of the beheading of German national Jurgen Kantner by the Abu Sayyaf group. - Islamic militants in the Philippines have beheaded the German hostage they were holding for ransom, the government in Manila said February 27. (Photo by NICKEE BUTLANGAN / AFP)