Shiite Iran offered Saturday to consider working with longtime foe the United States if it takes the lead in helping push back Sunni Arab militants who have seized a swathe of northern Iraq.
The offer came as Iraqi commanders said the army was preparing a fightback north of Baghdad, bolstered by thousands of Shiite volunteers who have signed up in response to a call to arms by top cleric Grand Ayatollah Ali al-Sistani.
Prime Minister Nuri al-Maliki visited the besieged shrine city of Samarra north of the capital Friday to rally troops and pray at the Al-Askari mausoleum, a revered Shiite shrine whose 2006 bombing by Al-Qaeda sparked sectarian conflict that killed tens of thousands.
President Barack Obama said he was "looking at all the options" to halt the offensive that has brought jihadist-led militants within 50 miles (80 kilometres) of Baghdad city limits but ruled out any return of US combat troops.
"We will not be sending US troops back into combat in Iraq, but I have asked my national security team to prepare a range of other options that could help support Iraqi security forces," he said.
Obama has been under mounting fire from his Republican opponents over the swift collapse of the Iraqi security forces, which Washington spent billions of dollars training and equipping before pulling out its own troops in 2011.
Iranian President Hassan Rouhani, who since his election last June has overseen a rapprochement with a superpower it long derided as the "Great Satan," said his government was prepared to consider offering help.
"If we see that the United States takes action against terrorist groups in Iraq, then one can think about it," Rouhani told a press conference.
- Maliki gets unlimited powers -
The Iraqi cabinet has granted the Shiite premier "unlimited powers" to reverse the lightning offensive, which has seen the militants sweep down towards Baghdad after overrunning second city Mosul on Tuesday.
A colonel from the military command responsible for Samarra, a city 110 kilometres (70 miles) north of the capital, said reinforcements from the federal police and army arrived on Friday.
The officer said the reinforcements were for a drive against areas north of the city, including Dur and Tikrit, that militants seized in their drive south earlier this week.
Security forces were awaiting orders to begin, the colonel said.
On Friday, police and residents expelled militants from the Dhuluiyah area, just 90 kilometres (60 miles) north of Baghdad, where they had set up checkpoints, witnesses said.
"Residents are now firing into the air" in celebration, witness Abu Abdullah told AFP.
Security forces have generally performed poorly, with some abandoning their vehicles and positions and discarding their uniforms.
But they have been bolstered by a flood of volunteers since  Sistani urged Iraqis Friday to join up to defend the country.
A representative of Sistani, who is adored by Shiites but rarely appears in public, made the call from the shrine city of Karbala, south of Baghdad.
"Citizens who are able to bear arms and fight terrorists, defending their country and their people and their holy places, should volunteer and join the security forces to achieve this holy purpose," the representative said.
Obama said that while the United States was willing to help out, Iraq needed to take steps to heal the deep divide between the Shiite-led government and the Sunni Arab minority, whose resentment has been exploited by the jihadists.
"The United States will not involve itself in military action in the absence of a political plan by the Iraqis that gives us some assurance that they're prepared to work together," Obama said.
"We won't allow ourselves to be dragged back into a situation in which, while we're there. we're keeping a lid on things and, after enormous sacrifices by us, as soon as we're not there, suddenly people end up acting in ways that are not conducive to the long-term stability of the country."
"Any action that we may take to provide assistance to Iraqi security forces has to be joined by a serious and sincere effort by Iraq's leaders to set aside sectarian differences."
Pentagon spokesman Rear Admiral John Kirby declined to say what kind of response was being prepared.
He confirmed that the US aircraft carrier USS George H.W. Bush and its strike group were in the region and ready to act. The US navy said the carrier group was in the Arabian Sea.
State Department deputy spokeswoman Marie Harf dismissed criticism from Republican lawmakers that a residual US force would have stopped the Iraqi army from collapsing.
"When we left Iraq, after years of sacrifice and American taxpayer money, and certainly our troops felt that sacrifice more than anyone, the Iraqis had an opportunity," Harf told reporters.
Instead, Iraqi leaders "created a climate where there were vulnerabilities when it came to the cohesion of the Iraqi army," Harf said.