MANILA - President Rodrigo Duterte's appeal to rebel forces to join his government's fight against terrorists in Mindanao could be strategic in his efforts to forge peace with them, a former military chief said Tuesday.

Duterte, in calling for help from the Moro Islamic Liberation Front (MILF), the Moro National Liberation Front (MNLF), and the New People's Army (NPA), put these communist and Muslim rebels on the defensive, according to General Dionisio Santiago, former Armed Forces of the Philippines' chief of staff.

"Saan ka pupunta ngayon? Tinatawag ka. You are asked to assist government. If you refuse to do so, tapos icha-challenge mo pa ang government, then you are giving me a reason to go beyond Mindanao," he said in an interview with ANC's Early Edition.

(Where will you go now? You are being called, you are asked to assist government. If you refuse to do so, and then you will challenge the government, then you are giving me a reason to go beyond Mindanao.)

"Akala ko ba gusto niyong tumulong, gusto niyo ng peace, nagrereklamo kayo? Bakit you want to wage war? Let us wage war together against this very special group na walang kinikilala na," he added.

(I thought you wanted to help, you wanted peace, you kept on complaining about it? Why would you want to wage war? Let us wage war together against this very special group which recognizes no one.)

Duterte over the weekend said he would treat communist and Muslim rebels the same as state forces if they help the government fight extremist groups.

"I will hire you as soldiers - same pay, same privileges, and I will build houses for you in some areas," the President said during a visit to an army base in Jolo, Sulu.

National Democratic Front senior adviser Luis Jalandoni said the communist rebellion opposes the Maute and Abu Sayyaf for attacking civilians.

"In that sense, the CPP-NPA would be together with the Duterte government in opposing the Maute Group and the Abu Sayyaf," he said.

Meanwhile, Duterte met with MILF Chair Al Haj Murad Ibrahim and other members of the group in Davao City on Monday. Also present in the meeting were members of the government peace panel and AFP Chief of Staff General Eduardo Año.

Details of the meeting have yet to be disclosed but the agenda is believed to be the MILF's support for martial law in Mindanao.

Martial law was declared over the entirety of Mindanao after clashes erupted between government forces and the Maute group in Marawi City last week.

Firefight is still ongoing in different parts of the Lanao del Sur capital, and has so far caused at least 100 casualties.