The Islamic State (Isis) linked Filipino terrorist group, Abu Sayyaf, have killed 18 Philippine soldiers in a day of heavy fighting on the troubled Basilan Island. Officials added that a further 52 troops had been injured by the Muslim extremists in the largest single-day government combat loss of life in 2016.

The infamous Abu Sayyaf was founded in 1991 in Basilan, about 550m (880km) south of Manila and gave bayah (or pledged allegiance) to IS (Daesh) leader Abu Bakr al-Baghdadi in July 2014. According to reports from the island the troops were sent on Saturday 9 April to kill or capture Abu Sayyaf commander Isnilon Hapilon.

The extremists are thought to be behind a number of bombings and kidnappings in the country. According to the AP the clashes occurred in the hinterlands bordering Tipo Tipo and Al-Barka towns on the island province.

According to the reports just four militants were killed in the operation which took place as the nation marked the Day of Valor – which remembers all of the Filipinos who died in the Second World War. The military has been battling Muslim separatist rebels as well as Marxist guerrillas on the Sulu Archipelago.

According to the official, the militants were able to amass around 100-150 fighters very quickly, allowing them to inflict large casualties on troops, the officials said. The US have blacklisted Abu Sayyaf as a terrorist organization for a string of deadly bombings, extortion, kidnappings for ransom, and gruesome beheadings of locals and foreigners, including Christian missionaries.

On 8 April, Rolando del Torchio, a former priest turned businessman, was finally released by the insurgents after six months in captivity. He was released following protracted negotiations with his kidnappers.

In March Abu Sayyaf hijacked an Indonesian vessel taking 10 crew members hostage. The Indonesian navy confirmed the boat has been seized by the militants, based on nearby Jolo Island, and the government said they have received a ransom demand from the captors – although it is not clear if the demands had been met as of yet.