Two years after the Philippine city of Marawi was overrun by jihadists it remains in ruins, with experts warning that stalled reconstruction efforts are bolstering the appeal of extremist groups in the volatile region.

The May 23, 2017 invasion by gunmen waving the black flag of the Islamic State group sparked a five-month battle that shattered swathes of the southern city.

Demolition of blast-pocked buildings has finally begun, but after several false starts the government does not expect rebuilding to be finished before the end of 2021.

The delays have left about 100,000 residents in squalid relocation camps or sharing homes with relatives, feeding simmering anger among the displaced and providing a recruiting tool for extremists.

"The narratives (to join IS) used to be about the Middle East and the plight of Muslims around the world," said Mouhammad Sharief, who co-founded a support group for Marawi's youth.

"Now it's closer to our hearts because the narrative is Marawi," said 32-year-old Sharief, who was himself displaced by the fighting.

Marawi is symbolically important because it is the Muslim capital of the nation's south, which has been locked in a cycle of poverty and extremism as separatist insurgencies have raged for decades.

It is all the more significant as IS works to maintain a presence via its global affiliates following the fall of its self-proclaimed "caliphate" in the Middle East.

IS regularly claims responsibility for killings of Philippine government troops and took credit for the January bombing of a Catholic cathedral during Sunday mass that was the nation's deadliest attack in years.

- Duterte's orders -

The organization has links to local extremist networks, including the kidnap-for-ransom group Abu Sayyaf, that have long operated in the Philippines' restive south.

In this context, an angry displaced population in Marawi is not a risk that can be ignored, experts say.

"The government needs to be concerned about the threats of ISIS attracting young (locals) because of the ongoing resentment from the failure to rebuild and general anger over the destruction," analyst Sidney Jones told AFP.

Fixing the city has been repeatedly delayed. A Chinese-led consortium initially tapped to spearhead the rehabilitation plan was disqualified over legal and financial issues.

The clearing of debris, the first step before the actual construction, also hit a snag due to legal problems and the government hopes it will finally be finished in November.

"This will be used as an example again of government discrimination against Muslims and the government neglect for the responsibility of rebuilding Marawi," said Francisco Lara, an adviser with peace group International Alert.

The government says it is making progress in repairing the city, which was pounded by military air strikes and artillery as it struggled to dislodge the jihadists.

"We are following the guidance and instructions of the president that he will see to it that Marawi will rise as a prosperous city again," Eduardo del Rosario, a retired general overseeing the rebuilding efforts, told journalists this week.

"We... are all undertaking the task given to us as per instruction of the president," he added.

Though President Rodrigo Duterte has tried to portray himself as sensitive to the Philippines' Muslim minority, he has sent mixed signals about Marawi.

He has claimed the city was home to illegal drug activity, a very serious accusation from a leader whose narcotics crackdown has killed over 5,300 alleged dealers and pushers.

"I don't think that I should be spending for their buildings. People there have a lot of money," he said in reference to Marawi in an April speech.