With only three days to go before the deadline for parliament to approve the constitution, Shias and Kurds reached agreements on Friday on some points such as the name of the country, Islam as the state religion and the ethnically-mixed city of Kirkuk, Kurdish legislator Mahmoud Othman said.
But Sunni Arab politician Saleh al-Mutlaq was very pessimistic about reaching an agreement by the Monday deadline, saying "matters are very complicated and need divine intervention".
Othman said Shias and Kurds have agreed that the country be called the Iraqi Federal Republic and that Islam be the religion of the state.
He said Shias and Kurds, who hold majority seats in parliament, were giving concessions to each others.
On the other hand, Iraq's three major Sunni organisations appeared to have taken a united stand both for voting and against demands for federalism after they boycotted the 30 January parliamentary elections.
One of the groups is the Iraqi Islamic Party, the largest Sunni Arab political party which has members on the committee drafting the constitution.
At the Kmeira Mosque in Baghdad's northern neighbourhood of Rashdiyah, about 500 Sunni Arabs gathered to listen to party member Shaikh Ayad al-Izzi say "we reject these calls [for federalism] and we look to them with suspicion".
During a speech on Thursday to cheering crowds in the city of Najaf, Abdul-Aziz al-Hakim, leader of the country's biggest Shia party, called for a Shia federal state, saying it was needed "to keep a political balance in the country" after decades of dictatorship under Saddam Hussein.
Al-Hakim's comment drew a strong response from Sunni clerics throughout Iraq during Friday sermons.
Abdul Aziz al-Hakim: Federalism
is needed for a political balance
Al-Mutlaq, the Sunni member of the constitution drafting committee, said they have told the Shias and the Kurds that if they put federalism in the constitution, "it will be rejected by the people."
He said the Sunnis are under heavy pressure from the Americans to finish the document before Monday. "They won't even accept an extension of days, or even hours, so that they can tell their people 'we have finished our mission,"' al-Mutlaq said.
He said the Americans suggested on Friday that federalism be included in the constitution but discussed by the parliament to be elected in December.
"We reject that. We want decentralisation now and then people can decide about parliament," he said.
Sunnis urge voting
Sunnis were preparing their people to go out and vote.
"We call our sons to go out and register their names so that they can take part in the coming referendum on the constitution and the general elections," Shaikh Fakhri al-Qaisi told a congregation in Saddam Hussein's hometown of Tikrit, 130km north of Baghdad.
Al-Qaisi told worshippers at Tikrit's Grand Mosque: "We should all go out and vote."
The Shia and Kurd are accused of
giving concessions to each other
Shaikh Mahmoud al-Sumaidaie, of the influential Association of Muslim Scholars, told worshippers at Baghdad's Umm al-Qura mosque to register for the referendum and 15 December, general elections because "we are in need to your voice to say 'yes' for the constitution or 'no'."
"We, in this country, don't want federalism because we are a unified nation in this country and we feel that Iraq with all it's elements is for all" of us, al-Sumaidaie said.
Shia, Sunni and Kurdish political leaders have been discussing several points of disagreement, including federalism, for days.
The Sunni Arabs appear to be sending a warning that they can bring down the constitution in the 15 October referendum.
"We, in this country, don't want federalism because we are a unified nation in this country and we feel that Iraq with all it's elements is for all"
Shaikh Mahmoud al-Sumaidaie,
Association of Muslim Scholars
According to the country's interim charter, if two thirds of the people in three provinces vote against the constitution it will be considered void.
Sunni are the majority in the provinces of Anbar, Salahuddin, Ninevah and Diyala.
Al-Izzi, of the Kmeira Mosque, said "don't sit at home because by staying at home it means you are accepting. We will say no to anything that contradicts with our religion and we will say no to anything that leads to splitting the country."