CIVIL SOCIETY groups say they hope the new UN human rights envoy is "not too diplomatic" in his new posting, saying on the eve of his first visit to the Kingdom that a balance has to be struck between negotiation and criticism.

Surya Subedi, a Nepalese national, is likely to change tack from his predecessor Yash Ghai, who resigned from the post in September after enduring multiple personal attacks from government officials.

But local rights groups have warned against submitting to UN "soft" diplomacy, saying the position requires some sting.

"There is no one in the country who can say the things that this person can," said Sok Sam Oeun, director of the Cambodia Defenders Project.

Subedi, a professor of international law at the University of Leeds, is to meet with rights advocates during his 10-day tour, including the director of the Cambodia Centre for Human Rights, Ou Virak.

"I'm not sure how diplomatic you can be and at the same time do this job," Ou Virak said Sunday.

"The question he will need to address is, What is the role of the UN human rights envoy? If it is to address human rights abuses, then you can't be too diplomatic," he added. Subedi is also expected to meet several senior members of the government during his visit.