An air strike has killed three Muslim extremists from a group linked to Al-Qaeda in the restive southern Philippines, a military spokesman said Sunday.

The three members of the Abu Sayyaf group were found dead after air force planes attacked their outpost on the strife-torn southern island of Jolo on Saturday, according to Colonel Randolph Cabangbang.

The attack came after military intelligence said that a feared Abu Sayyaf leader, known as "Doctor Abu", had been spotted in a forested region in Jolo.

"We have been going after them long before but we needed solid information before we could launch an operation," Cabangbang told AFP.

Two rifles were recovered along with the three bodies and the search for the rest of the extremist gang continues on the island, a longtime haunt of the outlaw group, the colonel said.

The Abu Sayyaf is a group of Islamist militants founded in the 1990s, with seed money from Osama bin Laden's Al-Qaeda network, that numbers only a few hundred armed men but is blamed for the country's worst terrorist attacks.

The group has carried out numerous kidnappings for ransom and bombings, often targeting Christians and foreigners.

The assault on Jolo comes after two weeks of fighting, including artillery and air strikes, against other Muslim armed groups in the southern Philippines.

Cabangbang said the air strike on Jolo was not linked to the attacks elsewhere, mainly against groups linked to the Moro Islamic Liberation Front (MILF), the country's main Muslim rebel group.

However another military official warned the MILF that sheltering "lawless elements" would make it the target of armed operations as well.

"These ongoing operations are intended for lawless elements only and not the MILF," said national military spokesman Colonel Arnulfo Burgos in a statement issued in Manila.

"However if the MILF coddles or provide sanctuary to these lawless elements, they will become legitimate targets too of the law enforcement operations," he warned.

In previous weeks, military and police pursuit of outlaws in a marshy, coastal region in Zamboanga Sibugay province and in the nearby island of Basilan have turned into pitched battles with MILF-linked forces.

As many as 40 soldiers, police and civilians were killed in the clashes which sparked angry public calls for "all-out war" against the MILF.

The 12,000-strong MILF eventually disowned the armed band involved in the Zamboanga Sibugay fighting but have blamed the military for the deaths of 19 soldiers in Basilan, saying they intruded on rebel territory.

Despite the public anger, both President Benigno Aquino and the MILF have separately said they are still committed to a peace process aimed at ending a decades-old rebellion that has left 150,000 dead since the 1970s.

However the Abu Sayyaf are not covered by the talks or the ceasefire.

Hundreds of US soldiers have been stationed in the region for a decade to train the local military to fight the Abu Sayyaf.

In September 2009, two US troops working on a school project were killed by an improvised explosive device in Jolo believed to have been planted by the Abu Sayyaf.