MANILA, Philippines - Abu Sayyaf, an Islamic militant group from the southern Philippines notorious for abducting foreigners, was reported to have killed a second Canadian hostage on Monday.

Canadian Prime Minister Justin Trudeau said he had "compelling reasons to believe" that Robert Hall, abducted nine months ago, had been murdered.

Canada gov't believes hostage has been killed in PH

Here are five facts about the Abu Sayyaf:

ORIGINS

The group is a radical offshoot of a Muslim separatist insurgency that has claimed more than 100,000 lives in the south of the mainly Catholic Philippines since the 1970s.

It was established in the 1990s with funds from a relative of former Al-Qaeda leader Osama bin Laden.

Abu Sayyaf's strongholds are the Muslim-populated islands of Jolo and Basilan in the far south of the Philippines, about 1,000 kilometres (600 miles) from Manila.

METHODS

Sallying forth in fast boats from the islands, the Abu Sayyaf snatches local and foreign victims, demanding ransom payments for their freedom.

Hostages, many of them Western tourists but also Christian missionaries and locals, are then hidden among sympathetic Muslim communities on Jolo and Basilan.

Victims are often murdered if ransoms are not paid -- the Abu Sayyaf beheaded an American man in 2002, a Malaysian last year, and another Canadian man in April who was abducted at the same time as Hall.

US HELP

The United States lists the Abu Sayyaf as a "foreign terrorist organization".

From 2002-2014, the US deployed Special Forces advisers to train and provide intelligence to Filipino troops, which led to the killing or arrest of many Abu Sayyaf leaders.

US assistance was scaled back after the Pentagon concluded the group, originally with about 1,000 fighters, had lost the ability to launch international attacks.

RISING THREAT

Since then, the Abu Sayyaf has launched a series of raids on foreigners and locals, as well as engaged in battles with Filipino troops that have killed dozens from both sides.

A German couple abducted from their yacht in 2014 were released after six months, with a ransom of more than $5 million believed to have been paid.

The Abu Sayyaf has abducted 44 Filipinos and foreigners since last year in at least 16 separate incidents, according to Pacific Strategies and Assessments, a regional risk assessment organisation.

BLACK FLAGS

In recent years, several Abu Sayyaf units, along with other small armed groups in the south, have publicly pledged allegiance to the Islamic State group that holds vast swathes of Iraq and Syria.

IS, known for its black flag and brutal interpretation of Islamic law, has acknowledged them and cited the Abu Sayyaf in its communiques and news reports.

Philippine authorities and security analysts say the pledges are just ploys to draw attention and potential funding from IS. They say the Abu Sayyaf is less interested in Islamic ideology than in getting rich from kidnappings.

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