Saleh al-Mutlaq said he stood by claims that Iraq was becoming a new dictatorship under Mr Maliki and predicted Iraqis could rise up violently if he remained in his post.
“The longer al-Maliki stays in power, the higher the possibility of a divided Iraq,” Mr Mutlaq said during an interview at his office in Baghdad.
A spokesman for Mr Maliki dismissed his comments, saying they are “not worthy of a response”.
Mr Mutlaq’s Sunni-backed Iraqiya party has been boycotting parliament and cabinet meetings since last month in protest at what it sees as efforts by the prime minister to consolidate power, particularly over state security forces.
Mr Maliki’s government, meanwhile, has demanded the arrest of the country’s top Sunni politician, vice-president Tariq al-Hashemi of Iraqiya, accusing him of running a hit squad targeting government officials.
Mr Hashemi, who remains holed up in Iraq’s semiautonomous northern Kurdish region, denies the allegations.