MANILA, Philippines ? The beheading of a kidnap victim is the latest proof that a small number of Islamic militants in the Philippines are defying a sustained US-backed military campaign to extinguish them, observers say.
The grisly development this week came just ahead of US Secretary of State Hillary Clinton's visit to the Southeast Asian nation, throwing the spotlight on joint efforts by Filipino and American forces to crush the Abu Sayyaf.
"The Abu Sayyaf are still well-entrenched in the jungle. They are capable of mounting terrorist attacks," said Rommel Banlaoi, executive director of the Philippine Institute for Political Violence and Terrorism Research think-tank.
"They have funds to buy bomb ingredients and train potential bombers."
The Abu Sayyaf was founded in the 1990s with seed money from Osama bin Laden's Al Qaeda-network to fight for an independent Muslim state in the south of the mainly Catholic nation, analysts say.
The militants, who have never numbered more than 1,000, operate in remote and often lawless islands of the southern Philippines, resorting to kidnappings for ransom and other crimes to raise funds.
US Special Forces advisers first arrived in the volatile southern Philippines to train and equip the Filipino military to combat the Abu Sayyaf in 2001.
It was part of then US president George W. Bush's so-called "war on terror," and the jungles of Basilan and Jolo islands were seen as an important part of the Southeast Asian theater.
Only a few hundred US troops have been in the south at any time, according to the Philippine military, and they have been active in building infrastructure as part of a development push alongside the training.
Philippine authorities say the Abu Sayyaf's numbers have fallen from about 1,000 eight years ago to 300-400 now, thanks to the military campaign.
US intelligence and weaponry have helped Filipino soldiers capture or kill the main leaders of the Abu Sayyaf early in the mission, but younger, more radical rebels have taken their place, according to Banlaoi and other analysts.
And despite the military crackdown, the group continues to carry out brutal attacks.
Clashes in the southern islands since the start of the year have left 48 Filipino soldiers and at least 70 Abu Sayyaf militants dead, according to a tally by Agence France-Presse based on authorities' reports.
In September, two US soldiers were killed in a roadside bomb in the deadliest attack by the Abu Sayyaf so far on the American contingent.
And on Monday the Abu Sayyaf dumped the severed head of a school principal they kidnapped in October on Jolo Island, a gruesome reminder of their chilling brutality.
Julkipli Wadi, an Islamic studies professor at the University of the Philippines who has closely followed the Abu Sayyaf, said a constitutional ban on foreign troops joining combat mission had tied the Americans' hands.
"If the gauge of success is the elimination or neutralization of the Abu Sayyaf, then it would appear that the cooperation has been a failure," Wadi said.
Philippine military intelligence officials told AFP the Abu Sayyaf has over the years built up funding through kidnapping and extortion, while moonlighting as drug couriers.
More than 80 percent of its members are below 25 years of age, many of whom are high-school drop outs lured by promises of monetary rewards from criminal activities by the group, the officials say.
The government's chief negotiator for the Muslim insurgency, Nabil Tan, said the Abu Sayyaf also took advantage of the bitter memories Jolo Muslims still felt from an American campaign of pacification in the early 1900s.
In 1906, American general John 'Blackjack" Pershing's army killed over 1,000 Jolo Muslims who refused orders to disarm some years after Spain ceded the islands to the United States at the end of the Spanish-American War.
Suicidal Muslim fighters were defiant, forcing Pershing to commission the making of the .45 caliber handgun because the .38 revolver appeared to have little effect on them.
"Their [US military advisers'] presence is seen as a challenge by the local militants. People still remember General Pershing to this day," said Tan, who is also a native of Jolo.