MANILA (2nd UPDATE) - If Communist Party of the Philippines (CPP) founding chair Jose Maria Sison decides to visit the Philippines to participate in the peace talks, President Rodrigo Duterte guaranteed Thursday said the communist leader may still go back to exile if peace negotiations fail.

“I have invited Sison to come home. He has agreed. I gave him a window of two months, very small. Make or break tayo dito… I will see to it and will personally maybe escort him to the airport if nothing happens in two months. I will allow him to go out. I will not arrest him because that’s word of honor,” Duterte said in a mix of Filipino and English.

Duterte, once a student of Sison at Lyceum university, however, said he will “kill” Sison if the latter returns here despite failed talks.

“But I will tell him, ‘You s** o* a b****, don’t ever return here. I will kill you. If nothing happens, I will tell him, ‘Do not ever, ever return again to this country. I will kill you. You’ve killed so much of my soldiers and policemen.”

Sison, in a statement Thursday, said he will not return to the Philippines on a whim and place himself "at the mercy of Duterte".

"Hindi basta basta ako umuwi at ilagay ko ang sarili ko at entire peace nego sa bulsa at awa (mercy) ni Duterte at mga reaksyonaryo at militar na pumpalibot sa kanya. Dapat substantial progress muna sa peace nego bago mapag-iwanan ang foreign neutral venue na safe and convenient for the negotiators and consultants of both sides," he said.

"Kung ang crucial nego ay gagawin sa Pinas, may peligro ito na manggulo ang mga peace spoilers at peace saboteurs, tulad ng pagdukot at pagpaslang sa sinumang mayor na panelist o consultant ng NDFP."

Sison, who fled to Europe after peace talks failed in 1987 and has stayed abroad since, has said he is ready to go home as soon as there is "substantial progress" in peace negotiations between communist rebels and the government.

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Sison earlier revealed that an interim peace agreement is expected to be signed when formal talks between the government and the National Democratic Front of the Philippines resume on June 28.

Both sides, Sison said, were expected to announce a stand-down agreement two weeks before that.

"So, by June 14, plantsado na (it's all ironed out)," he said. "Of course, I may be proven wrong because everything depends on that joint announcement... but I don’t see any problem because there may be some misunderstanding but they can be solved."

The talks fell through in November last year following clashes between government troops and communist rebels.

President Rodrigo Duterte then moved to have the CPP-New People’s Army declared as a terrorist group.

Duterte, however, had a change of heart, saying he would like to give peace another chance.