BAGHDAD (REUTERS) - Iraqi Prime Minister Nouri al-Maliki said on Wednesday he is committed to forming a new government on time as he fights growing calls from his opponents, and some of his former allies, to step aside.

A mounting Sunni insurgency is threatening to rupture Iraq 2-1/2 years after the withdrawal of U.S. troops, and Mr Maliki's domestic opponents say he has made matters worse by alienating moderate Sunnis who once fought al Qaeda but are now teaming up with the extremist Islamic State in Iraq and Syria (ISIS).

"We will attend the first session of parliament in harmony with the constitutional merits and out of the commitment to the call of the Supreme Marjaiya (Iraq's Shi'ite clergy) and out of loyalty to our people," Mr Maliki said on state television.

On Friday, the Marjaiya's Grand Ayatollah Ali al-Sistani himself called for the government formation process to begin.

Last Wednesday, the results of an April national election were certified, triggering a process that means the first parliament session must be held by July 1.

U.S. Secretary of State John Kerry said that in a meeting with Maliki on Monday the premier had "on multiple occasions affirmed his commitment to July 1" as the date to start forming a new government.

While U.S. officials have been careful not to say publicly they want Maliki to step aside, Iraqi officials say such a message was intimated behind the scenes.