The new charter passed by a simple majority after opponents failed to muster the two-thirds majority in three of Iraq's 18 provinces necessary to block ratification, commission spokesman Farid Ayyar said.
The outcome of the 15 October referendum finally hinged on the results of the mainly Sunni northern province of Nineveh which was among the last provinces to declare its results.
Two other Sunni majority provinces had already voted against the charter by the necessary two-thirds majority but Nineveh voters only rejected the text by 55% to 45%, insufficient to block its adoption.
Spokesman of the Iraqi National Dialogue Council, Salih al-Mutlaq, called for repeating the referendum in some governorates under international and Iraqi judicial supervision.
Speaking to Aljazeera on Tuesday, al-Mutlaq said that results of the referendum had been forged in some governorates.
"We believe that the results have been forged in Mosul, Diyala and most southern Iraqi governorates," he said.
"We call for repeating the referendum in Diwaniya, Samawa, Mosul and Diyala governorates under UN and Iraqi judicial supervision."
One Iraqi group has called for a
repeat of the vote in some areas
Al-Mutlaq added: "We will recognise the constitution in this case only; otherwise, this constitution then represents an extreme failure in Iraq and we do not recognise it."
Sunni Arabs, who dominated Saddam Hussein's and all previous Iraqi governments, generally opposed the new constitution, fearing its federal nature would leave the country's vast oil resources in the hands of Kurds and Shia.
Approval of the constitution paves the way for legislative elections in December, although lawmakers are to convene a body to consider further changes to the basic law under an accord hammered out before the referendum.
Yes (%) No (%)
Al-Anbar (capital Ramadi)
Arbil (Arbil) 99.36 00.64
Babil (Hilla) 94.56 05.44
Baghdad (Baghdad) 77.70 22.30
Basra (Basra) 96.02 03.98
Dhi Qar (Nasiriyah) 97.15 02.85
Diyala (Baquba) 51.27 48.73
Dohuk (Dohuk) 99.13 00.87
Karbala (Karbala) 96.58 03.42
Misan (Amara) 97.79 02.21
Muthanna(Samawa) 98.65 01.35
Najaf (Najaf) 95.82 04.18
Nineveh (Mosul) 44.92 55.08
Qadisya (Diwaniya) 96.74 03.26
Salah al-din (Tikrit) 18.25 81.75
Al-Sulaimaniya (al-Sulaimaniya) 98.96 01.04
Tamim (Kirkuk) 62.91 37.09
Wasit (Kut) 95.70 04.30
About 15.5 million Iraqi voters were asked whether or not they approved the new charter that places considerable power in the hands of regional authorities, and enshrines Kurdish autonomy in the north.
The Shia are expected to form a similar autonomous region in central and southern Iraq.
The charter adoption is considered important in any decision about the future withdrawal of US-led forces from Iraq.
Nationwide, 78% of voters said "yes" to the charter, above the simple majority required. Voter turnout was 63% of eligible voters.
Election results showing Iraqis have ratified a new US-backed constitution by a large margin are accurate and should be trusted, a senior UN official said on Tuesday.
Speaking after Iraq's Electoral Commission released final results showing 79% approval for the constitution in the 15 October referendum, Carina Perelli said the balloting process adhered to the highest standard.
"Yes, it has been audited, controlled. It has been done really in a very professional way," Perelli, head of the UN team providing technical assistance to the Iraqi government, said.
"The result is accurate. It has been checked according to the processes that we all follow when we have elections."
Japan welcomed the adoption by a majority of voters of Iraq's new constitution, and urged Iraqi officials to overcome their religious and ethnic differences to cooperate in future political process.
Japan's Foreign Minister Nobutaka Machimura said in a statement that the approval "is an extremely important development in the political process in Iraq."
"Our country hopes future political process, including upcoming parliamentary elections, will progress through cooperation that goes beyond religious and ethnic differences."
The Italian government on Tuesday also welcomed the Iraqi referendum vote in favour of the new constitution and promised to continue to support the establishment of democracy in the country.
Machimura hopes for better
relations between Japan and Iraq
"The success of the referendum is the start of a new era of dialogue and reconciliation between all Iraqis, despite the ethnic and religious differences and shows that politics has defeated terrorism and its violence," said Italian Foreign Minister Gianfranco Fini in a message to his Iraqi counterpart Hoshyar Zibari.
"My country has supported the electoral process with strength and conviction and will continue to do so," Fini said.
The White House on Tuesday called the approval of Iraq's constitution "a landmark day" for efforts to build democracy in the war-torn country and hailed robust rates of voter participation.
"It's a landmark day in the history of Iraq. We congratulate the Iraqi people," spokesman Scott McClellan told reporters after the charter won support from nearly four out of five Iraqis who cast ballots.
Britain hailed the result as a milestone and looked forward to "maximum participation" in elections to be held in two months' time.
"The Iraqi people have shown again their determination to defy the terrorists and take part in the democratic process," said Foreign Secretary Jack Straw.
The UN envoy to Iraq on Tuesday called the approval of Iraq's constitution a "major advance" but highlighted the ethnic divisions reflected in the vote.
"The people of Iraq have demonstrated their commitment to a credible, inclusive and peaceful political process which augurs well for the December elections and the future of the country," UN envoy to Baghdad Ashraf Qazi said in a statement.
"The results of the referendum have indicated the degree of political polarisation in Iraq," the UN statement said. "This poses an ongoing challenge for all Iraqis and underscores the importance of an inclusive national dialogue."