Baghdad Four of the most senior political leaders in Iraq's fragile coalition have threatened to bring a vote of no-confidence in the government unless "autocratic decision-making" stops, a letter published in a state newspaper on Saturday said.

Iraq's Shiite, Sunni and Kurd coalition began to creak in December, after US troops left, when the government tried to remove Sunni Deputy Prime Minister Saleh Al Mutlaq and issued an arrest warrant for Sunni Vice-President Tareq Al Hashemi.

Those incidents intensified long-running tensions between the Sunni and Shiite blocs that have hampered the government's ability to pass key legislation.

The Baghdad government and the autonomous Kurdish region are also engaged in a simmering row over oil exports.

The four senior lawmakers — Osama Al Nujaifi, Masoud Barzani, Eyad Al Alawi and Moqtada Al Sadr — sent the letter to Prime Minister Nouri Al Maliki's bloc on Thursday, political sources said.

Some of Al Maliki's opponents, including Barzani and Al Sadr, have accused him of becoming a dictator and several of his critics say he deliberately sidelines Sunnis and Kurds.

The letter outlines eight demands to be met by May 13 to ensure the four leaders' support for Al Maliki's administration.