UPDATE 1-Philippine army camp blast kills 5; Islamic State claims responsibility

* Blast sets back Duterte's bid to crush extremists
* Islamic State says suicide bombers infiltrated base
* Jolo a stronghold of Islamic State-linked Abu Sayyaf

(Recasts with Islamic State claim, higher death toll, adds
context, background)
MANILA, June 28 (Reuters) - An explosion at a military base
in the restive southern Philippines on Friday killed five
people, including three soldiers, and wounded nine others in
what Islamic State said was an attack by its suicide bombers.
The military said the blast occurred at around noon at a
base on Jolo island, a stronghold of the Abu Sayyaf, a
splintered militant network notorious for kidnapping and piracy
and for its pledge of allegiance to Islamic State.
Islamic State said via its Amaq news agency that its
fighters had infiltrated the base strapped with explosives and
killed or wounded 100 soldiers. It posted an image of two young
men standing beside a black Islamic State flag, wearing what
appeared to be vests designed to hold explosives.
Neither the claim nor the authenticity of the photograph
could be immediately verified.
The incident will be a major setback for Philippine
President Rodrigo Duterte's goal of wiping out Abu Sayyaf, for
which he has created a special infantry division on Jolo to be
comprised of 4,500 troops by 2022.
There was no immediate comment from Duterte's office.
The army provided few details of what took place, but vowed
a thorough investigation and to respond "with formidable
resolve".
"Ground troops continue to establish the circumstances and
identify the perpetrators behind this inhumane attack," said
Cirilito Sobejana, chief of the Western Mindanao Command. "We
will intensify our offensives to crush terrorist groups."
Clashes between troops and Abu Sayyaf have intensified in
the wake of a January bombing of a Jolo church that killed 21
people and wounded close to 100, among them soldiers and
civilians. Islamic State also claimed responsibility for that
assault. Duterte has maintained martial law across the Mindanao
region to curb Islamic State's influence and the decades of
banditry by Abu Sayyaf, which is known for its brutality and for
posting videos of captives begging for their lives, and for
beheading those for whom ransom demands are not met.
A Dutch wildlife photographer held hostage by Abu Sayyaf
since 2012 was killed last month by his captors when he tried to
escape during a firefight with troops, according to the
military, which said six rebels were killed.