'We warn that any such step will not be acceptable to the majority of Iraqis and will have dangerous consequences,' said the 73-year cleric, who has been assuming a larger role in politics although he does not favor a theocracy in Iraq.
Annan said last week he would send a team to Iraq as soon as possible to help form an interim government in response to an invitation from the U.S.-installed Iraqi Governing Council.
Sistani had criticized Brahimi and Annan for a report they wrote, which agreed with U.S. authorities that general elections needed months of preparation and were not feasible considering a lack of security.
The Shi'ites wanted elections before June 30, the date Washington set to hand back sovereignty to an unelected Iraqi government.
The report angered Sistani and millions of his followers eager to take power after political dominance over Iraq by Sunni Arabs, a minority concentrated in central Iraq.
Under the interim constitution, which was passed earlier this month, elections are due by 2005.
Sistani said the interim constitution was unworkable because it establishes a three-person presidential council composed of a Sunni Muslim, a Kurd and a Shi'ite Muslim who would be required to take unanimous decisions.
'This builds a basis for sectarianism. Consensus would not be reached unless there is pressure from a foreign power, or a deadlock would be reached that destabilizes the country and could lead to break-up,' Sistani said.
My biggest problem with the interim constitution is Chapter 7. I'll put up my piece on that in the next day or so.
I guess the most important question about the constitution's paralytocracy is raised by al-Sistani. If the system only works in the presence of a foreign power, who is that likely to be? We already have Gen Abizaid saying he will resolve any disputes and we have Article 59 allowing him to do that.