REPUBLIKA.CO.ID, MARAWI CITY -- Australia agreed on Friday to send two surveillance planes to help the Philippines tackle Islamist rebels, as jets and artillery pounded militant positions in a southern town held for more than a month by Islamic State loyalists.

The Philippines accepted the offer of two AP-3C Orion aircraft for reconnaissance to pinpoint locations of Maute group fighters holed up for a fifth week in Marawi, a town the rebels have declared as their own Islamic territory.

"The regional threat from terrorism, in particular from Daesh and foreign fighters, is a direct threat to Australia and our interests," Australian Defence Minister Marise Payne said in a statement, referring to Islamic State by an Arabic acronym.

Australia's help comes as fears grow that the Maute and its affiliates have much stronger designs on parts of the southern Philippines than previously imagined, evidenced by their preparations and combat capability during the weeks of fighting.

The threat is heightened by losses suffered by Islamic State in Syria and Iraq, and intelligence reports that it is building alliances and seeking new pastures from which to project its agenda.

Gilbert Gapay, an Philippine military spokesman, said the surveillance planes would help tackle extremism across Mindanao, an island of 22 million people, where separatists, pirates and kidnap gangs have thrived for decades.

He said the battle for Marawi was not a failure because the military had learned a lot and was stopping Islamic State from taking root.

"This gives us a picture of the expanse of their network," Gapay told reporters.

"They won't thrive anymore in our country."

But security experts say the battle has exposed intelligence and operational failures by the Philippines and its limited cooperation with neighbouring Malaysia and Indonesia to stop extremism from spreading.

The three countries on Thursday agreed on joint measures to pool information and try to stem recruitment, movement and financing of fighters. The Philippines says it knows of 40 foreign operatives in the country.

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