Philippine authorities marked Wednesday the first anniversary of the siege by Islamic State-inspired militants of the southern city of Marawi that disrupted the lives of hundreds of thousands of people, underscoring the importance of drawing lessons from it to avoid a repeat.

Interior Secretary Eduardo Ano, who was military chief during the months-long battle for Marawi, told reporters that it is "very important" to recall the events of a year ago as a reminder that if all concerned had done their jobs in fighting terror, then "this kind of crisis should not have happened at all."

President Rodrigo Duterte himself has admitted lapses in intelligence ahead about the massing of Maute and Abu Sayyaf militants in the predominantly Muslim city on Mindanao Island with the objective of setting up an Islamic caliphate.

Duterte responded to the militants' takeover of parts of the city on May 23 by ordering an all-out offensive against them and imposing martial law across Mindanao.

The fierce battle for the city ended in October with nearly a thousand militants dead, including Abu Sayyaf leader Isnilon Hapilon, who was regarded as the emir of Islamic State in Southeast Asia, as well as Maute Group leaders Omar and Abdullah Maute. More than 160 soldiers and policemen, and 47 civilians also died.

The war displaced more than 350,000 people and severely destroyed the city, especially its commercial center. The cost of damages is estimated at 11.5 billion pesos (over $219 million), while economic loss is 6 billion pesos.

The planned rehabilitation of the city, which is intended to come up with a much better Marawi than its previous state, will require at least 72 billion pesos.

"Even before the start of the siege, if the information (about the presence of hundreds of armed men) from the residents, or even from village officials, or even from the local government had reached (authorities), we would have prepared much better," Ano lamented.

"As early as April 2017, we had received information already that some armed personnel had gained entry there. But no one reported where these armed men specifically went. Even with the arrival of Hapilon, they still did not report that."

Zia Alonto Adiong, a local official, said the crisis in Marawi already had a preview when authorities had run-ins with the Maute Group in 2016 in the neighboring town of Butig, and then in Piagapo.

Ano acknowledged some lapses also of tactical commanders on the ground in assessing raw information about the militants' plans.

With those in mind, Ano said there is a whole-of-government approach now in preventing and countering violent extremism, involving even the Education Department, among many other agencies, as well as the religious sector.

"The imams (Islamic leaders) have a responsibility also in guiding people using religion. What happens normally is, if some missionaries arrive, we just let them be, not knowing they are already extremist missionaries," he said.

In his message for the first anniversary, Defense Secretary Delfin Lorenzana said, "Let us ever be vigilant in protecting our communities."

Military spokesman Col. Edgard Arevalo said the armed forces continue to monitor reports about efforts of Maute Group remnants to recruit, reorganize and regroup. The military, he said, is actively working to thwart this.

"Let's learn from the lessons of Marawi," presidential adviser on the peace process Jesus Dureza said.

Marawi City Mayor Majul Gandamra, speaking in a press conference in his home city, said, "Last year, on this very day, many of us fled our homes in fear and grief. Now, a year after, we're back here with hope and determination to move forward."

"We have reason to feel optimistic because the great outpouring of help and love from the nation and beyond has been overwhelming," he added.