In the course of their nine-year battle with Maoist rebels, "Nepali security forces have established themselves as one of the worlds worst perpetrators of enforced disappearances," the group said in a report.

It said local human rights groups had recorded more than 1,200 disappearances in the past five years alone.

"Given the scale of disappearances we have documented, the heightened role of the army after the kings seizure of power is frightening," said Brad Adams, Asia director of the New York-based group.

Gyanendra a month ago sacked the government and declared emergency rule, saying the previous ruling coalition could not deal with the rebels who are fighting to establish a communist republic in the world's only Hindu kingdom.

Shortly after the power grab, the king made an offer of unconditional peace talks to the rebels, who had branded him a "national betrayer". Security forces said the guerrillas face tough action if they refuse the call.

"Maoist forces have a horrendous record of killings, torture and intimidation, but the response cant be to unleash an army that has been responsible for so many disappearances and other egregious human rights abuses," Adams said.

The international community should act immediately to prevent a deepening "disappearances" crisis in the wake of the royal takeover, he added.

The 171-page report documents more than 200 enforced disappearances it says were perpetrated by Nepal's army and police.

The group said its research had indicated that the actual number of "disappearances" may be significantly under-reported since many families feared to approach the authorities.

In almost all cases documented in the study, witnesses claimed that individuals who "disappeared" had last been seen in the custody of security forces, who had rounded them up in large scale operations, at checkpoints, on the streets or from their places of work or study.