RIO DE JANEIRO, Dec 27 (Reuters) - A group representing two-thirds of bondholders in Brazilian miner Samarco have rejected a restructuring offer put forth by the company, though both sides are expected to offer fresh proposals, according to separate statements released on Monday. Samarco, a joint venture between BHP Group (BHP.AX) and Brazil"s Vale SA (VALE3.SA), was granted bankruptcy protection by a Brazilian court in April and has been negotiating with bondholders since. A previous proposal put forth by the company was rejected by bondholders in July. read more A tailings dam at a Samarco-owned mine burst in 2015, killing 19 and provoking a severe environmental disaster. The mine has only recently begun operating again, leaving Samarco with a considerable debt load.