The Australia-based Fiji Democracy and Freedom Movement has expressed its concern about a former parliamentarian, Peceli Rinakama, who has not been seen since last Friday.
Reports say he was seized by soldiers, but the military and the interim government have declined to comment on the matter.
As his whereabouts remain unknown, the Movement's Usaia Peter Waqatairewa has accused the interim regime of failing to guarantee the safety of its citizens.
"We are very concerned that this politician has disappeared for five days going on to six days now, and we havenot had any word from anybody."
During the recent trial of eight men accused of plotting to kill the interim prime minister, the court was told that Mr Rinakama was gathering ex-military personnel for the cause.
He was not among those made to stand trial but was briefly held in 2007 in connection with the alleged plot.