The Islamic militant group Abu Sayyaf has long been seen as the most radical of the separatist movements in the southern Philippines.
Philippine troops launched a new offensive last August
Estimated to have fewer than 300 core members, it has made up for its small size by the ruthlessness of its actions - kidnapping Western tourists for ransom and carrying out various high-profile bomb attacks.
But with the recent deaths of two senior Abu Sayyaf leaders, analysts are wondering whether the group might now be a spent force.
President Gloria Macapagal Arroyo recently said a "mortal turning point" had been reached in the fight against this shadowy organisation.
"They're definitely a much diminished threat than they once were, and they're on the run right now," agreed Professor Zachary Abuza, a US-based expert on South East Asian militant groups.
But while Abu Sayyaf has definitely been set back, there is still some doubt about whether more militants will emerge from the lawless jungles of the southern Philippines to fill the gaps.
"They're not just going to give up - it's still relatively easy for them to find new recruits," said Prof Abuza.
Abu Sayyaf - which means Sword of God in Arabic - began as a splinter group from the less radical Moro National Liberation Front (MNLF) in 1991.
The military recently announced the death of Abu Sulaiman
Led by the now deceased Afghan Mujahideen veteran Abdurajak Abubakar Janjalani, it quickly established a reputation for using extreme tactics to further its aim of establishing an Islamic state in the southern Philippines, especially on the island of Jolo.
Abu Sayyaf has long been a thorn in the side of the Philippines military, and an offensive against the group in 2002 - called Operation Endgame - clearly failed to live up to its name.
But since US-backed Philippine troops launched a new operation last August, dubbed Oplan Ultimatum, they have netted several major Abu Sayyaf figures.
First Khaddafy Janjalani - the group's nominal leader and brother of Abdurajak Janjalani - was reported to have been killed in September. DNA tests confirmed the death on 20 January.
Then came the news last week that another key member, Abu Sulaiman, had been fatally wounded in a gun battle.
Both had $5m bounties on their heads, but analysts agree that, of the two, Sulaiman's death was probably the most significant because he was behind so many of the group's major plots and attacks - including the bombing of a passenger ferry in 2004, which killed at least 100 people.
"Abu Sayyaf will definitely have difficulties finding someone with the leadership skills of Abu Sulaiman," said military spokesman Lieutenant-Colonel Bartolome Bacarro.
The army says that so far, Oplan Ultimatum has "neutralised" five senior Abu Sayyaf leaders as well as about 70 other members.
Abu Sayyaf is "disorganised and suffering from a major leadership vacuum," said Lt Col Bacarro. "We will keep up the tempo and take advantage of that. We're confident we can finally put an end to the menace of Abu Sayyaf."
Ethnic and family ties
But killing isolated militants - even senior ones - is very different from getting rid of an organisation.
According to Prof Abuza, people living in the region often provide support for Abu Sayyaf militants, and do not make a huge distinction between them and separatists from other, less radical, groups, such as the MNLF and MILF (Moro Islamic Liberation Front).
"Clan and familial ties are more important than anything else in that part of the Philippines," said Prof Abuza.
The area has a long history of banditry and piracy and is a fertile militant recruiting ground due to grinding poverty, high unemployment and resentment caused by an influx of new Christian arrivals into an otherwise predominantly Muslim region.
Khaddafy Janjalani was killed in September
The need to improve the area's economy is acknowledged by the government, with presidential spokesman Ignacio Bunye saying recently that he was "determined to eliminate pockets of poverty in the area, to deprive extremists of recruiting grounds".
Another factor complicating the military's desire to vanquish the Abu Sayyaf is its close links to other separatist organisations in the region.
Although the MNLF technically signed a ceasefire with the government 10 years ago, that agreement has still not been properly implemented on the ground, and there are frequent reports of rogue MNLF splinter groups, disillusioned by the peace deal, providing sanctuary to Abu Sayyaf rebels.
This presents a problem for the Philippine military, which cannot enter MNLF compounds under the terms of the agreement.
Abu Sayyaf's relationship with the MILF is more complex, according to Prof Abuza. The MILF - which is currently holding peace talks with the government - denies links with Abu Sayyaf, but there are many reports to the contrary.
The other group with links to Abu Sayyaf is the regional militant network Jemaah Islamiah. The US-backed offensive in August was launched partly because of reports that one of that group's key figures, Indonesian terrorism suspect Dulmatin, was in the southern Philippines.
While militants with the bomb-making experience of Dulmatin would certainly be of use to a struggling group like Abu Sayyaf, he too is thought to be on the run.
Philippines troops have already found what was assumed to be his hideout, and also captured his wife and children.
"If he had a sanctuary, he could help Abu Sayyaf, but at the moment he's just in the jungle somewhere," said Prof Abuza.
There is no question that Oplan Ultimatum has so far made real progress in tracking down the shadowy leaders of Abu Sayyaf, in the way that no other operation has before.
"I've never seen the AFP (Armed Forces of the Philippines) have anything like the success it's having now," said Prof Abuza.
Analysts say this is at least partly down the help of the US soldiers in the area, who do not take part in active combat but provide training and equipment to local soldiers.
But however good the military might, it needs to be matched with economic progress and peace-building on the ground, so that currently weak groups such as Abu Sayyaf are not able to win over new recruits and regain their former strength.