Maliki, who left power in 2014 following heated pressure from the United States, has been chosen by Iraq's largest Shiite bloc, which would put him in line to be nominated prime minister.

Rubio, in a telephone call with incumbent Prime Minister Mohammed Shia al-Sudani, voiced hope the next government will work to make Iraq "a force for stability, prosperity and security in the Middle East."

"The secretary emphasized that a government controlled by Iran cannot successfully put Iraq's own interests first, keep Iraq out of regional conflicts or advance the mutually beneficial partnership between the United States and Iraq," Rubio said, according to State Department spokesman Tommy Pigott.

A pro-Iranian government in Iraq would be a rare boon for Tehran's clerical state after it suffered major setbacks at home and in the region.

The Islamic republic has killed thousands of Iranians since mass protests erupted in late December.

Since the October 7, 2023 attacks, Israel has hit Iran both with strikes inside the country and heavy blows against Tehran's Lebanese ally Hezbollah, while Iran lost its main Arab ally with the fall of Bashar al-Assad in Syria.

An Iraqi political source told AFP that the United States had conveyed that it "holds a negative view of previous governments led by former prime minister Maliki."

In a letter, US representatives said that while the selection of the prime minister is an Iraqi decision, "the United States will make its own sovereign decisions regarding the next government in line with American interests."

The United States wields key leverage over Iraq as the country's oil export revenue is largely held at the Federal Reserve Bank in New York, in an arrangement reached after the 2003 US invasion that toppled Saddam Hussein.

Chief among US demands is that Iraq prevent a resurgence of Shiite armed groups backed by Iran. Sudani, who took office in 2022, has won US confidence through his delicate efforts to curb violence by the groups.

Maliki initially took office in 2006 with support of the United States as he strongly backed US military efforts against Al-Qaeda in Iraq and other Sunni militants.

But the United States eventually soured on Maliki, believing he pushed an excessively sectarian agenda that helped give rise to the Islamic State extremist movement.

Iraq's parliament meets Tuesday to elect a new president, who holds a largely ceremonial role but will appoint a prime minister.