In Udhaim, 90 km (60 miles) north of Baghdad, Asaib and police fought militants who earlier occupied the local municipal building, an official there told Reuters, and they directed mortar fire at the government protection force of the Baiji oil refinery, Iraq's largest.
Masked jihadists under the black flag of ISIL aim to revive a medieval caliphate that would span a fragmenting Iraq and Syria, redrawing borders set by European colonial powers a century ago and menacing neighbours like Iran and Turkey.
The White House said on Saturday that Obama had called national security adviser Susan Rice on Friday night and on Saturday morning to receive updates on the situation in Iraq.
"The president directed her to continue to keep him appraised of the latest developments, as his national security team continues to meet through the weekend to review potential options," White House spokesman Josh Earnest told reporters.
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Kerry, in his call with Iraqi Foreign Minister Hoshyar Zebari, emphasized "that assistance from the United States would only be successful if Iraqi leaders were willing to put aside differences and implement a coordinated and effective approach to forge the national unity necessary to move the country forward and confront the threat of ISIL," the State Department said.
The Iraqi Foreign Ministry said in a statement that Kerry pledged $12 million in assistance and stressed that Baghdad should assure its neighbours the war is not sectarian, but against the insurgents.
Iranian President Hassan Rouhani, asked at a televised news conference whether Tehran could work with the United States to tackle ISIL, said: "We can think about it if we see America starts confronting the terrorist groups in Iraq or elsewhere.
"We all should practically and verbally confront terrorist groups," added Rouhani, a relative moderate who has presided over a thaw in Iran's long antagonistic relations with the West.
A senior Iranian official told Reuters earlier this week that Tehran, which has strong leverage in Shi'ite-majority Iraq, may be ready to cooperate with Washington against ISIL rebels.
The official said the idea of cooperating with the Americans was being mooted within the Tehran leadership. For now, according to Iranian media, Iran will send advisers and weaponry, although probably not troops, to boost Baghdad.
U.S. officials said on Friday there had been no contact with Iran over the crisis in Iraq. Asked about Rouhani's comments on Saturday, a White House spokesman said he would have no further comment.
Any initiative would follow a clear pattern of Iranian overtures since the 2001 al Qaeda attacks on U.S. targets, which led to quiet U.S.-Iranian collaboration in the overthrow of the Taliban in Afghanistan and formation of a successor government.
The United States and Iran, adversaries since Iran's 1979 revolution toppled the U.S.-backed Shah, have long accused each other of meddling in the Gulf and beyond, and have not cooperated on regional security issues for more than a decade.
Maliki: Beginning of end for militants
Militants attacked the convoy of the custodian of the holy shrine in Samarra, while he was en route to Baghdad. Sheikh Haider al-Yaqoobi was not harmed, but 10 of his guards were killed, a source in Samarra hospital said.
Maliki travelled on Friday to Samarra, one of the cities targeted - alhough not seized - by ISIL fighters who now prevail in a string of Sunni cities and towns running south from Mosul.
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"Samarra will not be the last line of defence, but a gathering point and launchpad," he told military officers after Iraq's most influential Shi'ite cleric urged people to take up arms and defend the country against the insurgents.
"Within the coming hours, all the volunteers will arrive to support the security forces in their war against the gangs of ISIL. This is the beginning of the end of them," Maliki, a Shi'ite Muslim, said in comments broadcast on Iraqi television.
Maliki said the Cabinet had granted him unlimited powers to confront insurgents. Last week, parliament failed to convene for a vote on declaring a state of emergency due to a boycott by most Sunni and Kurdish lawmakers.
In Basra, Iraq's main city in the mainly Shi'ite far south, hundreds volunteered to join the battle against ISIL, heeding a call to arms by Grand Ayatollah Ali al-Sistani, who commands unswerving loyalty from most Iraqi Shi'ites.
Iran's Rouhani said he would review any request for help submitted by Maliki, although none had been received yet. "We are ready to help in the framework of international regulations and laws," he said.