Hutu rebels are to be integrated into the Tutsi-dominated military

The electoral register will not be ready in time for the vote to be held as planned on 22 December, a commission spokesman said.

The vote is seen as a key step towards ending Burundi's decade-long civil war.

The draft constitution sets out a power-sharing arrangement designed to satisfy both ethnic Hutu rebels and the Tutsi-led army.

This is the third time that the referendum has been delayed. A new date has not been set.

Elections, which were due in November cannot be held until the new constitution is approved.

Slow disarmament

"The major reason for this new delay is problems with the electoral list, we want to avoid cheating," Paul Ngarambe, the chairman of the Independent Electoral Commission (IEC), said.

The peace process has already dragged on for more than four years.

It offers hope that the 10-year civil war - which has cost some 300,000 lives - may finally be coming to an end.

Even now, some parties from the Tutsi minority say the new system does not give them enough guarantees - and although all but one of the Hutu rebel groups have agreed to a ceasefire, the process of disarming former rebels and integrating them into a new army is well behind schedule.