"The majority of Sudanese will vote for secession if they have the chance to vote."
Decisions 'need to be made'
The SPLM's military also accused the government in Khartoum of transferring aid to rebel groups in the south. James Hoh, the SPLM's army chief, accused the Sudanese government of trying to push the south "in[to] turmoil".
The referendum is a key part of the 2005 peace deal that ended a decades-long civil war between north and south Sudan. Southerners are widely expected to vote for independence.
David Gressly, the top United Nations official in southern Sudan, said the commission needs to quickly get to work.
"We are not yet to the point where it [the referendum] can't occur on time," Gressly told the Associated Press news agency. "But some practical decisions will need to be made quickly."
Residents in the Abyei region, which sits on the likely border between north and south Sudan, will vote on independence in a separate referendum. But the commission to oversee that vote has not even been formed yet.
A coalition of NGOs warned last month that the Sudanese government and the UN are "alarmingly" unprepared for the referendum.