One of Iraq's most influential Shiite clerics, Moqtada Sadr, claimed Friday that jihadists were poised to attack Baghdad and he vowed to send his men to defend the capital.
"There are terrorist groups that have completed their preparations for a breakthrough into Baghdad," the cleric said in a statement.
"We are ready to defend the city, we are ready to supply forces and coordinate with the authorities to face any scenario," said Sadr, who announced the creation of the Saraya al-Salam (Peace Brigades) group in the aftermath of the jihadist offensive that began in June.
The force includes former fighters from his now dissolved Mahdi Army that fought US troops 10 years ago.
US jets were back in Iraqi skies Friday after President Barack Obama announced he had ordered food drops to civilians stranded in the north after being displaced by jihadist attacks.
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He also said he authorised air strikes against IS positions to ensure the safety of US assets in Kurdistan, after the Sunni extremist militants moved to within striking distance of the autonomous Kurdish region.
The Iraqi army chief of staff, Lieutenant General Babaker Zebari, told AFP he thought US jets would extend their campaign against other towns held by IS but he did not say which ones.
IS has controlled parts of Syria for some time and while it had bases in Iraq, it launched a major offensive on June 9 which saw it conquer much of Iraq's Sunni heartland and allow for the proclamation of a "caliphate" straddling both countries.
Jihadists stopped their offensive a few dozens kilometres from Baghdad and experts have generally said the capital was safe from a takeover that would require numbers IS does not have.
The main flashpoints with large IS presence around Baghdad are Jurf al-Sakhr, about 50 kilometres (30 miles) to the south, Fallujah, the same distance to the west, and a string of towns about 70 kilometres to the north.