Iraq's most-revered Shiite cleric called on the country's political blocs to agree on a prime minister in the next four days, putting pressure on a government that is struggling to address the growing security crisis.

The call Friday by Grand Ayatollah Ali al-Sistani came as Human Rights Watch said the Islamic State of Iraq and Syria, the Sunni extremist group that now controls large parts of Iraq, likely executed at least 160 unarmed men when it took the city of Tikrit.

NPR's Alice Fordham is reporting that Sistani's spokesman, Abdul-Mahdi al-Karbalaie, said in the holy city of Karbala that Iraq's political blocs should agree on who's going to lead Iraq before Parliament meets Tuesday. Here's what she told our Newscast unit:

"Tuesday's session will be the first since an election in April, and comes as parties jostle to form the largest coalition and therefore the right to appoint the prime minister. After parliamentary elections four years ago, government formation took 10 months. International leaders have joined the religious establishment in urging haste this time around, as Sunni militants take more territory across the country."

NPR's Larry Kaplow profiled Sistani earlier this week, and he noted that Sistani "stays out of the limelight, rarely meets with Westerners and doesn't do interviews. But he has generally been a calming influence and often helpful to U.S. efforts in Iraq."

Last week, Sistani called for an Iraq government that would "avoid past mistakes and open new horizons toward a better future for all Iraqis." That statement was seen as a tacit criticism of the government of Shiite Prime Minister Nouri al-Maliki, who has been accused of marginalizing the country's minority Sunnis.

Maliki, whose party won a majority of votes in elections held before the recent gains made by ISIS, has criticized calls for a unity government, calling them a coup against the constitution and Iraq's democracy. He has also made clear that he isn't stepping aside without a fight. But he is under pressure, as even his most important ally, Iran, is looking for alternatives, according to The Associated Press. Here's more from the AP:

"A senior Iranian general who met with Shiite politicians in Iraq during a 10-day visit this month returned home with a list of potential prime minister candidates for Iran's leadership to consider, several senior Iraqi Shiite politicians who have knowledge of the general's meetings told The Associated Press on Thursday. The general, Ghasem Soleimani, is expected to return within days to inform Iraqi politicians of Tehran's favorite, they said, speaking on condition of anonymity to discuss the internal deliberations."

The political maneuvering came as fighting between Iraqi forces and ISIS continued. The AP reports that four helicopters with Iraqi commandos landed at a soccer pitch inside a university campus in Tikrit late Thursday and clashed with militants; also, 200 troops arrived at the Beiji refinery, Iraq's largest, which has been taken over by militants. Earlier this month, ISIS militants captured Tikrit as well as Mosul, one of Iraq's largest cities, with relative ease. But in the wake of their gains, they have left behind casualties.

Human Rights Watch, in a report released Friday and based on satellite imagery, said the insurgents killed at least 160 unarmed men in Tikrit. Alice has also been reporting on that story for Newscast. Here's what she said:

"Those killed may have been air force recruits, working on a local air base. But when the fighters from the extremist group known as ISIS captured them, they were wearing civilian clothes and unarmed. Footage posted by ISIS and analyzed by Human Rights Watch shows the masked extremists lining men up on the edge of a trench outside the town of Tikrit, and shooting them with automatic weapons. ISIS took Tikrit as they swept through northern and western Iraq almost two weeks ago. Residents in the Sunni-dominated area have long complained of ill treatment by the Shiite-led security forces. But they say they are fearful, too, of the brutality of ISIS."

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