The United Nations (UN) Human Rights Office has expressed concern that the disappearance of pastor Raymond Koh and activist Amri Che Mat is linked to their community work.

"We are gravely concerned for the safety and well being of the two men and we fear they may have been abducted due to their community work.

"We call on the Malaysian government to conduct a prompt investigation to establish their whereabouts and to keep their families informed of any developments," UN Human Rights Office acting regional representative Laurent Meillan said in a statement today.

Koh's family has previously brought the matter to the UN working group on enforced or involuntary disappearances (WGEID).

His wife, Susanna Liew, also said earlier today that she cannot rule out the possibility that her husband's case is an "enforced disappearance".

Enforced disappearances imply that the state is linked or is involved to the disappearances.

The UN Human Rights Office in its statement urged the Malaysian government to urgently sign and ratify the International Convention for the Protection of All Persons from Enforced Disappearance.

"Enforced disappearances are rare in Malaysia and it is deeply concerning that little progress has been made into these cases," Meillan said.

Koh's abduction, which took place on Feb 13, was caught on CCTV and it depicted eight masked men in three black SUVs abducting the pastor from his car.

Witnesses claimed that Amri's disappearance, which occurred on Nov 24, 2016, also happened in a similar way.

Amri had previously been accused of "deviant" Shia teachings in Malaysia while Koh was formerly investigated by religious authorities for allegedly proselytising to Muslims, said the UN Human Rights Office.