The general secretary of the Geneva-based organisation, Olav Fykse Tveit, said in the letter that he was “gravely concerned” over Koh’s safety.
He said he had been informed that Koh had been abducted in a “cruel and organised manner” that had been “equated to an act of terror”.
Mentioning some of the good community work Koh had been doing, Tveit added: “However, he has been accused of proselytising and has received threats on several occasions.”
Koh, 62, was driving to see a friend in Kelana Jaya on Feb 13 when he was abducted by a group of masked men on Jalan SS4B/10. CCTV footage that has since been making the rounds apparently shows he was abducted in a well-executed plan involving more than 10 men and seven vehicles in broad daylight.
In 2011, Koh’s NGO, Harapan Komuniti, had been accused of proselytising to Muslims by Islamic religious groups.
Tveit said: “It is highly appreciated that freedom of religion is enshrined in the Malaysian Constitution and the majority of people live in peace and harmony in your multicultural and multi-religious country.
“But this disturbing incident, which is causing deep anxiety and concern for the life and wellbeing of Pastor Koh, is also promoting fear and mistrust among the religious minorities.”
He ended the letter by saying: “Please give this appeal your personal urgent consideration.”
Police detained a 32-year-old man on Thursday in Ampang, Selangor, in connection with the abduction.
“The suspect contacted the victim’s family a day before his arrest and asked for money to secure the pastor’s release,” Selangor police chief Abdul Samah Mat had said in a statement.