SARANGANI - South Korea's envoy on Thursday said he accepted President Rodrigo Duterte's apology but called for a speedy and thorough investigation into the abduction and killing of businessman Jee Ick-joo allegedly by Philippine police.

Ambassador Jae-Shin Kim said many of his compatriots were "upset" and may now be "reluctant" to visit the Philippines following the incident.

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But he said Seoul was looking at ways to "control the damage" and "calm down the feeling of the people."

"This is an enormous shock to the Korean community," he told reporters after meeting with Duterte, who graced the ceremonial switch-on of a coal-fired power plant here.

"Of course, the Korean people are very, very upset and we are embarrassed such a heinous crime is committed."

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The Philippines is a popular destination for Korean tourists who spent P5.65 billion in November 2016 alone, according to the Department of Tourism.

Duterte on Thursday personally apologized to Kim, who was seated among the audience here, vowing that those behind the killing "will suffer."

"Better if they escape from prison. I'll send their heads to you," Duterte said in a speech.