The names of the "representatives" have not been made available, nor is it known who they represent or who has chosen them.
Billed as the country's first experiment with democracy in decades, the Association of Muslim Scholars (AMS) - the highest Sunni Muslim authority in the country - has already announced it will boycott the talks.
The AMS decision was not unexpected, according to the president of the preparatory committee, Fuad Maasum. The group has consistently refused to negotiate while a single US occupation soldier remains on Iraqi soil.
Maasum also confirmed that the conference was being boycotted by representatives of Shia leader Muqtada al-Sadr - though the invitation was still open.
"I invited the Sadr camp to attend ... I did not want to put Sayyid Muqtada in an uncomfortable position by inviting him personally, but the invitation is open to his movement."
An al-Sadr spokesman in June said the leader of the al-Mahdi army was planning to create his own political party to contest the first full elections in January.
The Shia leader also said the allocation of one seat out of 1300 at the conference did not sufficiently recognise an organisation with thousands of members.
But Maasum said the absence of al-Sadr's camp and the influential Sunni Muslim Committee of Muslim Scholars would not diminish the conference's legitimacy or significance.
"That is the political decision they have made and that is their prerogative," he said.
"I admit that the conference does not hold a magic wand to solve all of Iraq's problems in two or three days, but it will at least be a chance for the majority of Iraqis to agree on the nature of the transition process."
"I did not want to put Sayyid Muqtada in an uncomfortable position by inviting him personally, but the invitation is open to his movement"
president of the preparatory committee
Scant information has been provided by the interim government or by US officials in the capital. The scene in Baghdad reflects the lack of reporting - blocked roads, concrete barricades, tanks and sniffer dogs.
Baghdad shut down
Iraqi Interior Minister Falah al-Naqib also declared a curfew on the city centre to secure the safety of the unknown participants, starting on Sunday morning and lasting three days.
The government has imposed an 8am to 4pm daylight curfew in the old Karkh and Shaikh Maruf districts, adjacent to the Green Zone, for the duration of the conference expected to last until Monday or Tuesday.
The conference is to have limited legislative powers. It is to advise the selected interim government as it paves the way for national elections in January 2005.
The bulk of proceedings will be held in a large conference room inside the convention centre that was used under the previous government of Saddam Hussein to celebrate national holidays.
Only part of the proceedings will be transmitted live through closed circuit cameras to journalists in another conference room, organisers said.
The event is the brainchild of the dissolved US-led occupation authority and the United Nations, which has helped in its preparations and will oversee its workings.