Iraq's top Shiite cleric urged all of its people Friday to unite and expel Sunni Muslim insurgents, as Shiite Prime Minister Nuri al-Maliki came under growing pressure at home and abroad.
The call came after US President Barack Obama stopped short of acceding to Maliki's appeal for air strikes on the Islamic State of Iraq and the Levant (ISIL), prompting neighbouring Shiite Iran to charge that Washington lacked the "will" to fight terror.
A swift militant offensive, led by the jihadist ISIL, has overrun swathes of northern and central Iraq, threatening the United States's already damaged legacy in the country.
Grand Ayatollah Ali al-Sistani, a revered cleric whose stature dwarfs that of any other figure among the Shiite majority, called for Iraqis to band together against the insurgents before it was too late.
If ISIL is not "fought and expelled from Iraq, everyone will regret it tomorrow, when regret has no meaning," his spokesman announced on his behalf.
The reclusive Sistani, who heads a council of senior clerics, also said Iraq's next government must be "effective" and avoid "past mistakes", an apparent rebuke to Maliki, premier since 2006.
His remarks came after several senior American figures pushed the premier, who is seeking to retain his post after winning a plurality in April 30 elections, to work with Iraq's Sunni Arab and Kurdish minorities.
- US criticises Maliki -
US Vice President Joe Biden, Defence Secretary Chuck Hagel, Chairman of the Joint Chiefs General Martin Dempsey and David Petraeus, the former top US commander in Iraq, have all either called for Maliki to be more inclusive or outright criticised him.
Obama said Thursday Maliki's actions could dictate the country's fate, amid a growing feeling in Washington that the Iraqi leader would do best by moving on.
Former US ambassador to Baghdad James Jeffrey said there has been a "definite uptick" in Washington's criticism of Maliki.
"Everybody is a bit at fault in Iraq on the sectarian thing, but Maliki over time did become more" sectarian, said Jeffrey, who left the post in mid-2012.
"He just isn't the solution to a unified Iraq."
Obama, who based his political career on ending the costly eight-year US intervention in Iraq, has insisted that his country is not slipping back into the morass.
But he has offered as many as 300 military advisers and left open the possibility of "targeted and precise military action if and when we determine that the situation on the ground requires it".
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Washington has already positioned an aircraft carrier in the Gulf and is flying manned and unmanned surveillance flights over Iraq.
It is also still considering drone strikes against the militants.
Senior US officials said privately that special forces being sent to advise Iraqi forces could call in air strikes if necessary.
- Iran's derision -
The latest offer was the most concrete action announced by Washington since the crisis erupted on June 9. But it fell short of Iraq's request for air strikes and drew derision from Tehran, which has offered its cooperation despite decades of enmity.
"Obama's comments show the White House lacks serious will in fighting terrorism in Iraq and the region," Deputy Foreign Minister Hossein Amir Abdollahian said.
Iraqi security forces continued to battle militants in several areas Friday, with 34 members of the security forces killed in a town on the border with Syria.
Elsewhere, the battle for the strategic northern town of Tal Afar entered its sixth day. Witnesses said security forces clashed with militants, who still hold significant ground.
Shiite-majority Tal Afar is located along a strategic corridor to Syria, and the largest town not to fall to militants in the northern province of Nineveh, most of which has been overrun.
A senior army officer told AFP that Iraq needs US help.
"We need American support to stop terrorism and eliminate it... especially through air strikes against specific targets," the lieutenant general said, asking not to be identified.
Meanwhile, UN aid agencies said they were rushing supplies to Iraq to help more than one million people driven from their homes by the current fighting and unrest earlier this year.
Around 500,000 people have been displaced in the western Anbar province, notably the flashpoint city of Fallujah, since the beginning of this year, the UN says.
A similar number fled after the northern city of Mosul fell to ISIL last week, and tens of thousands have hit the roads in the eastern province of Diyala, near Baghdad, and Salaheddin, north of the capital.
Earlier this week, UN Secretary General Ban Ki-moon warned that the conflict threatened to spill over Iraq's borders, interlocking with the civil war in neighbouring Syria, where ISIL is also fighting.