The three - the General Conference for the People of Iraq, the Iraqi Islamic Party and the Iraqi National Dialogue - have been urging Sunnis to take part in the December 15 election.
They named their coalition the Iraqi Accord, said Ayad al-Samarrie, a senior official in the Iraqi Islamic Party.
Sunni Arabs, to whom belonged all the Iraqi presidents since the establishment of the Iraqi state in 1921, largely boycotted the January 30 election that produced Iraqi's current mostly Shia and Kurdish interim government.
But many Sunnis ignored calls by the country's mainly Sunni anti-US and anti-US backed government for a boycott of Iraq's October 15 constitutional referendum, with many of them going to the polls to vote "no".
After a 10-day audit cleared that vote of any fraud or serious irregularities, Iraq's election commission announced on Tuesday that the constitution had passed with a nearly 79% "yes" vote, thanks to big support by Shias and Kurds.
The new constitution is another step forward in Iraq's intended democratic reforms and it cleared the way for the December 15 election to choose a new Iraqi parliament.
The document also is part of the Bush administration's goal of one day withdrawing US forces after the formation an independent, democratic Iraqi government that can be protected by strong Iraqi security forces.
Some Sunnis have cast doubt
on the authenticity of the vote
Nearly all Sunnis voted against the constitution, fearing that it would break Iraq into two oil-rich nearly autonomous regions - a Kurdish one in the north and a Shia one in the south - and leave most Sunni in a weak district in central and western Iraq.
Tariq al-Hashimi, the general-secretary of the Iraqi Islamic party dismissed such allegations and said Sunni Arabs region contain the source of life of the Iraqi south where Shia live, which is water.
"If Sunnis are just fearing from being left without oil we would not have gone to the Shia and Kurds to ask them to change the constitution and make Iraq's natural resources under the control of the central government" he told Aljazeera.net.
"The constitution says every region controls its oil resources, and when we put our request the Shia and Kurds were astonished how we ask to put the Sunni region's resources under the central government, they told us this would deprive Sunni from controlling their rich-phosphate region," al-Hashmi said.
"The reason for that is we are after Iraq's unity, not money and domination. If it is about wealth, this is the least of our worries, we are rich enough."
None of the three moderate Sunni groups that formed the new Iraqi Accord coalition has seats in Iraq's current interim parliament because they boycotted last January's parliamentary elections.
The Iraqi Islamic Party, a main Sunni group, angered many Sunnis when it called for a last-minute "yes" vote to the constitution.
"We urged yes vote after we were ensured that the constitution will be revisable and changeable" al-Hashimi told Aljazeer.net.
"We urged yes vote after we were ensured that the constitution will be revisable and changeable".
Iraqi Islamic Party
The General Conference for the People of Iraq is an umbrella of Sunni political, religious and tribal groups. An official from the Iraqi National Dialogue took part in drafting the new constitution.
In another political development Wednesday, the Association of Muslim Scholars, an influential group of Sunni clerics, criticised the new constitution, saying it will only "benefit the occupiers and those who collaborate with them".
"The whole process is designed by the US occupation, and it will definitely serve its interests" he said.
Reading an association statement to reporters, spokesman Abdul-Salam al-Kubaisi claimed "no" votes in the referendum had been blocked in a "big conspiracy against our Iraq".
For that reason, he said, "the association will not take part in any political process" in Iraq.
In Samara, a Sunni Arab city with minority Arab Shias, scores of Iraqis took the streets to protest the final results of the referendum on Iraq's new constitution.
Meanwhile, other political parties and personalities continued negotiations aimed at forging other alliances ahead of the December 15 parliamentary election.
Former Prime Minister Ayad Allawi, a secular Shia and former senior Baath Party member, was expected to announce his own coalition of Shias and Sunnis by the end of this week.