The appeal by Grand Ayatollah Ali al-Sistani came as the country seems increasingly in danger of falling apart, with the al-Qaeda breakaway group the Islamic State of Iraq and the Levant having seized much of northern and western Iraq and the Kurds asserting control over long-disputed territories outside their autonomous region.
Prime Minister Nouri al-Maliki's bloc won the most seats in April's election, but he is now fighting for his job, with even fellow Shiite allies and key patron Iran exploring alternatives to replace him.
But al-Maliki, who has governed the country since 2006, has proven to be a savvy and hard-nosed politician, and so far he has shown no willingness to step aside.
Less than three years after the last American troops left Iraq, Washington has found itself being pulled back in, with drones now flying over Baghdad to protect American civilians and newly deployed US military forces.
Washington has stopped short of demanding al-Maliki step aside, but in what is widely seen as veiled criticism of his divisive leadership, has called for a more inclusive government.
That has set the stage for what could be months of arduous coalition negotiations. After 2010 elections, it took Iraqi politicians nine months to agree on a new prime minister. Now, unlike four years ago, the territorial cohesion of Iraq is at stake.
Seizing on the sense of urgency, Sistani called on politicians to agree on the next prime minister, parliament speaker and president by the time the new legislature meets on Tuesday, a cleric who represents him said in a Friday sermon.
