The coalition contains 40 political parties and groupings and will pit al-Maliki, a Shia, against the ruling Shia-dominated bloc, from which the premier broke away in August.

History of shifting

Al-Maliki had chosen not to join the recently formed, mostly Shia, Iraqi National Alliance (INA) opting instead to form a multi-confessional bloc.

The INA is headed by the Supreme Islamic Iraqi Council (ISCI), a powerful Shia party which has ties to Iran. It includes the movement of the fiery anti-US cleric Muqtada al-Sadr and a few Kurds and Sunnis.

Mohammed al-Bayati, an ISCI member, and analysts said there could be some partnership between the INA and State of Law after the election.

"We wish them success... A national front will be formed in the next parliament in participation with the INA," al-Bayati said.

Iraqi political groupings are fluid and alliances have shifted dramatically in the past.

Hameed Fadhel, an analyst at Baghdad University, said: "No side is likely to get a majority, and there will be a need for partnerships after the results. Such talk before then is difficult because I think there will be heated competition."

The split in al-Maliki's and ISCI's Shia political bloc, now the biggest in parliament, is likely to deepen tensions in a country still plagued by violence.

Yet it could also mark a maturing of Iraq's democracy if there was a credible shift away from the sectarian and identity politics which has defined Iraq's legislative system to date.