Karim Kadim, Associated Press
Followers of Shiite cleric Muqtada al-Sadr attend open-air Friday prayers in the Shiite stronghold of Sadr City, Baghdad, Iraq, Friday, July 25, 2014.

BAGHDAD — Iraq's most influential Shiite cleric, Grand Ayatollah Ali al-Sistani, has called upon political leaders not to "cling" to their posts at the cost of political stability as pressure mounts for Prime Minister Nouri al-Maliki to step down.

"The gravity of the phase Iraq is undergoing requires the concerned parties to bear their national responsibilities, which require sacrifice and not to cling to posts," the reclusive al-Sistani said in a statement read by his spokesman Abdul-Mahdi al-Karbalaie at Friday prayers in the holy city of Karbala.

"This government... should enjoy wide national acceptance so that it will be able to face the current challenges, correct the accumulating mistakes of the past and unite people in order to combat terrorism," the speech read.

Al-Sistani did not name specific leaders. Last month, however, the cleric called on al-Maliki through an intermediary to step aside in the face of a crisis sparked by the lightning advance by Sunni militants, according to a senior member of a prominent Shiite family that has for decades maintained regular contact with al-Sistani. Al-Maliki is currently seeking a third four-year term.

Iraq is facing its worst crisis since the 2011 withdrawal of U.S. troops following the blitz launched last month by the so-called Islamic State, an al-Qaida breakaway group which captured large swaths of land in the country's west and north, including Iraq's second largest city, Mosul.

Leaders are under pressure to form an inclusive government that can draw Sunni support away from the insurgency. But Sunnis have long accused al-Maliki of marginalizing their community, and even many of his Shiite and Kurdish allies say he has monopolized power.

On Thursday, Iraqi lawmakers named veteran Kurdish politician Fouad Massoum as the new president, a largely symbolic post. After taking the oath, Massoum noted the "huge security, political and economic tasks" facing the next government. The next step in Iraq's political transition will be for Massoum to select a candidate for prime minister who will try to form a new government.

Underscoring the urgency of the task faced by Iraq's leaders, a car bomb exploded outside a mosque near the northern city of Kirkuk as Shiite worshippers were leaving after Friday prayers, killing eight people and wounding another 24, according to police and hospital officials. The officials spoke on condition of anonymity because they were not authorized to brief the media.