Philippine President Rodrigo Duterte was preparing to make a deal with Islamic State-inspired militants in the days after they laid siege to a southern city, but aborted the plan without explanation, an intermediary involved in the process said.

Agakhan Sharief, a prominent Muslim leader, said that after a band of Islamist fighters overran parts of Marawi City on May 23 and took hundreds of people hostage, he was approached by a senior Duterte aide to use his connections with the Maute militant group's leaders to start back-channel talks.

Two other Marawi sources familiar with the matter confirmed the president had worked behind the scenes to hold talks with the Maute brothers, Omarkhayam and Abdullah.