Iraq's top Shia cleric has urged the UN not to endorse the Iraqi interim constitution, saying it could lead to the country's break-up.
Ayatollah Ali al-Sistani said he would not meet a UN team unless the world body took a "clear stance".
He said the three-person presidency - composed of a Shia, a Sunni and a Kurd - set up under the constitution would encourage sectarianism and partition.
The ayatollah's concerns held up the signing of the document in early March.
The constitution, approved by the US-appointed Governing Council, is a key step in the handover of power from the US-led coalition to Iraqis on 30 June.
It is a fundamental law that is supposed to govern Iraq during its transition period.
It seeks to establish a democratic government, while preserving the rights of the minority Sunnis and Kurds through a federal system.
Ayatollah Sistani - who represents the Shia majority - only agree to the document after expressing deep reservations.
'Divisions'
The BBC's Suzy Price, at UN headquarters, says his latest statement threatens to make any future UN role in Iraq even more complicated.
In a letter, the ayatollah's office said he would not meet the UN delegation unless it took "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 letter said the three-member presidency "enshrines sectarianism and ethnicity in the future political system in the country".
The interim document stipulates that decisions taken by the presidency must be unanimous.
UN Secretary General Kofi Annan said he needed to study the remarks before commenting.