While al-Maliki's State of Law bloc won the most seats in parliament in the Iraq's April 30 election, his hopes for a third term are now in doubt with rivals challenging him from within the broader Shiite alliance. In order to govern, his bloc must first form a coalition with other parties.
And with Iraq asking the U.S. for airstrikes to temper the militants' advance especially as the insurgents were said to be preparing Friday for another assault on the country's biggest oil refinery al-Maliki appears increasingly vulnerable.
"It is necessary for the winning political blocs to start a dialogue that yields an effective government that enjoys broad national support, avoids past mistakes and opens new horizons toward a better future for all Iraqis," al-Sisanti said in a message delivered by his representative Ahmed al-Safi in the Shiite holy city of Karbala.
The Iranian-born al-Sistani, who is believed to be 86, lives in the Shiite holy city of Najaf south of Baghdad. A recluse, he rarely ventures out of his home and does not give interviews. Iraq's majority Shiites deeply revere him, and a call to arms he made last week prompted thousands of Shiites to volunteer to fight against the Islamic State of Iraq and the Levant, which was once part of al-Qaida.
Al-Sistani's call to arms has given the fight against the Islamic State militants the feel of a religious war between Shiites and Sunnis. His office in Najaf dismissed that charge, and al-Safi on Friday said: "The call for volunteers targeted Iraqis from all groups and sects. ... It did not have a sectarian basis and cannot be."
Al-Maliki has been seeking to place the blame for the chaos on the Islamic State and not his perceived exclusion of the Sunnis. However, questions persist on how much support, if any, the Islamic State enjoys among the Sunni population in areas it now controls.
Ali Hatem al-Salman, a prominent tribal Sunni leader and a critic of al-Maliki, said Sunni tribesmen would eventually fight the extremist Islamic State.
Using the commonly used Arabic acronym for the Islamic State, he told The Associated Press on Thursday: "Daash themselves know that the tribes will push them out. ... There can't be any trust given to Daash."
Al-Maliki's Shiite-led government long has faced criticism of discriminating against Iraq's Sunni and Kurdish populations. But it is his perceived marginalization of the once-dominant Sunnis that sparked recent violence reminiscent of Iraq's darkest years of sectarian warfare after the 2003 U.S.-led invasion.
Iraq's newly elected parliament must meet by June 30 to elect a speaker and a new president, who in turn will ask the leader of the largest bloc to form a new government within 15 days.
Al-Maliki has been doing the prime minister job in a caretaker capacity since the April 30 election. While it is far from certain he would step aside, if he were to relinquish the leadership post, according to the constitution, the president assumes the job until a new prime minister is elected.
However, the president, Jalal Talabani, a Kurd, has been ill and getting treatment in Germany since 2012. So the vice president, Khudeir al-Khuzaie, a Shiite, should assume the prime minister's job until one is elected.
Shiite politicians familiar with the secretive efforts to remove al-Maliki said two names mentioned as possible replacements are former vice president Adel Abdul-Mahdi, a French-educated economist who is also a Shiite, and Ayad Allawi, a secular Shiite who served as Iraq's first prime minister after Saddam Hussein's ouster.
With Iraq in turmoil, al-Maliki's rivals have mounted a campaign to force him out of office, with some angling for support from Western backers and regional heavyweights. On Thursday, their effort received a boost from Obama, who said: "Only leaders that can govern with an inclusive agenda are going to be able to truly bring the Iraqi people together and help them through this crisis."
An "inclusive agenda" has not been high on the priorities of al-Maliki, however. Many of al-Maliki's former Kurdish and Shiite allies have been clamoring to deny the prime minister a third term in office, charging that he has excluded them from a narrow decision-making circle of close confidants.
Al-Maliki's efforts last year to crush protests by Sunnis complaining of discrimination under his Shiite-led government sparked a new wave of violence by militants, who took over the city of Fallujah in the western, Sunni-dominated province of Anbar and parts of the provincial capital, Ramadi.
Iraqi army and police forces battling them for months have been unable to take most areas back, and over the past week or so the militants have also taken over the cities of Mosul and Tikrit.
Less than three years after Obama heralded the end of America's war in Iraq, he said Thursday he was dispatching up to 300 military advisers to help quell the insurgency. They would join up to 275 being positioned in and around Iraq to provide security and support for the U.S. Embassy in Baghdad and other American interests.
But he was adamant that U.S. troops would not be returning to combat.
Despite the deteriorating conditions, Obama has held off approving airstrikes sought by the Iraqi government. The president said he could still approve "targeted and precise" strikes if the situation on the ground required it, noting that the U.S. had stepped up intelligence gathering in Iraq to help identify potential targets.
U.S. officials say manned and unmanned U.S. aircraft are now flying over Iraq 24 hours a day on intelligence collection missions.
Not all Shiites welcomed the announcement that more Americans were heading to Iraq.
A Shiite cleric, Nassir al-Saedi, warned that the 300 advisers would be attacked. Al-Saedi is loyal to anti-U.S. cleric Muqtada al-Sadr, whose Mahdi Army militia fought the Americans in at least two rounds of street warfare during their eight-year presence in Iraq.
"Our message to the occupier: ... We will be ready for you if you are back," he told a Friday sermon attended by al-Sadr supporters in Baghdad's Sadr City district.
Mohammed al-Khalidi, a Sunni lawmaker who favors a replacing al-Maliki's government with a more inclusive one involving Shiites, Sunnis and Kurds, said he thought "Obama's statement was balanced and reasonable."
"But," he added, "U.S. officials should be aware that the situation in Iraq needs an immediate remedy because Iraq is heading to the unknown."