Iraq's most influential Shiite Muslim (search) cleric has written to the top U.N. envoy to the country saying the country's U.S.-backed interim constitution was a recipe for the break up of the country, according to a statement released Monday.

In a March 19 letter to top U.N. envoy Lakhdar Brahimi, Grand Ayatollah Ali al-Husseini al-Sistani (search) said he would not participate in upcoming meetings with U.N. officials should the world body endorse the interim law.

"This constitution that gives the presidency in Iraq to a three-member council, a Kurd (search), a Sunni Arab (search) and a Shiite Arab, enshrines sectarianism and ethnicity in the future political system in the country," the Shiite leader's letter said.

It said the presidential system of the constitution "will lead to a dead end and puts the country in an unstable situation and could lead to partition and division."

The interim document stipulates that decisions by the three-man presidency must be unanimous.

Al-Sistani said he would boycott the U.N. mission "unless the United Nations takes a clear stance that the constitution does not bind the National Assembly and is not mentioned in any new Security Council resolution concerning Iraq."

The National Assembly is to be elected before the end of January.

On March 8, the U.S.-picked Iraqi Governing Council signed the temporary constitution, a key step in the handover of power from the U.S.-led coalition to Iraqis on June 30.

The charter enshrines Islam as one of the bases of law and outlines the shape of a parliament and a three-member presidency, as well as a federal structure for the country. Billed as the most liberal in the Arab world, it will remain in effect until the permanent constitution is approved in late 2005.

Al-Sistani issued a fatwa, or religious edict, after the signing that said the document would only gain legitimacy if it is endorsed by an elected National Assembly.

U.N. Secretary-General Kofi Annan said last week he was sending a U.N. team, headed by Brahimi, back to Iraq "as soon as possible" in response to an Iraqi request for help in organizing the political transition and general elections due by Jan. 31.

Al-Sistani has joined the Iraqi political process several times in the past, forcing the U.S.-led coalition that is currently running the country to drop or revise plans. The latest was this month when the cleric objected to the interim constitution, delaying the signing ceremony for three days.