Fourteen other soldiers were also wounded after the military launched a major offensive on the camp in the town of Ungkaya Pukan on the remote island of Basilan Wednesday, officials said.
The facility was overrun, but reports from the field said day-long clashes that followed were fierce and led to the heavy casualties, regional commander Major General Benjamin Dolorfino said.
Numerous home-made bombs, ready for detonation, were recovered along with 13 high-powered firearms, he said.
The fighting was the heaviest since at least 29 soldiers were killed in two separate clashes with the Abu Sayyaf in July and August 2007 -- with the bodies of 10 soldiers later being found mutilated.
The military "launched a decisive law enforcement operation targeting the Abu Sayyaf´s main training camp in the province", army spokeswoman Lieutenant Steffani Cacho said.
"Recovered from the camp were sizeable quantities of IEDs (improvised explosive devices) rigged to explode while others were ready for use," she said.
Soldiers who airlifted their fallen colleagues to a military base in nearby Zamboanga City said those who died were hit by sniper fire.
Fighting has ceased, General Dolorfino said, but troops were still clearing the area to ensure no insurgents remained.
Troops were also pursuing other Abu Sayyaf members, he added.
The Abu Sayyaf was formed in the early 1990s by Islamic firebrand Abdurajak Abubakar Janjalani upon his return from Afghanistan, where he fought the Soviets alongside Al Qaeda leader Osama bin Laden.
Janjalani formed the Abu Sayyaf (Bearers of the Sword) ostensibly to fight for an independent Islamic state.
He was however killed in a 1998 clash with police, and the group quickly degenerated into a terror organisation specialising in bombings and high-profile kidnappings.
The group has raised money by ransoming hostages but has also killed some, mostly through beheading, when they were not paid promptly.
While the Philippine military has killed and captured many Abu Sayyaf leaders -- partly with US assistance -- the extremists remained active and in January they held three international Red Cross workers hostage for several months.
Two hostages were freed in April while the last, Italian Eugenio Vagni, was released on July 12 after nearly six months in captivity.
The Abu Sayyaf is also believed to be working alongside some 30 foreign militants from the Jemaah Islamiyah (JI) who are operating in the southern Philippines.
The JI, blamed for the 2002 bombings in Bali, Indonesia that killed 202, is said to be working with the Abu Sayyaf in plotting bombings in this mostly Catholic nation of 90 million, intelligence officials earlier told AFP.
Filipino intelligence officials said JI militants may also have helped the Abu Sayyaf carry out a spate of bombing in Mindanao in July that killed eight people.
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