HRW's Andrea Berg said Niyazova was last seen leaving home and there has been no news of her since then.
"We are very concerned about the situation of Umida Niyazova," she said. "It's the fourth day now that we do not know about her whereabouts, the family does not know where she is and her lawyer does not know where she is and we are afraid that she is held at [the Interior Ministry] or [the Security Ministry] or that somebody just kidnapped her."
Niyazova was detained at the Tashkent airport in December when she returned to Uzbekistan after visiting Kyrgyzstan.
Police at the time also confiscated her computer and some computer discs.
