BAQUBA, Iraq: Iraqi officials worked Saturday to calm soaring tensions after the killing of 70 people at a Sunni mosque, as Washington branded the beheading of an American journalist a "terrorist attack."
The attack at the mosque in Diyala province Friday, which most accounts say was the work of Shiite militiamen, threatens to increase already-significant anger among Iraq's Sunni Arab minority with the Shiite-led government and to undermine an anti-militant drive that requires Sunni cooperation.
It came as the US, which is carrying out air strikes in Iraq against Islamic State of Iraq and Greater Syria (ISIS) jihadists, ramped up its rhetoric over the grisly killing of journalist James Foley, carried out by the group and shown in a video posted online.
Deputy National Security Advisor Ben Rhodes said the beheading of Foley "represents a terrorist attack against our country."
In an unanimous statement Friday, the UN Security Council condemned the murder as "heinous and cowardly."
On Saturday, Iraq's Sunni Arab parliament speaker sought to calm tensions caused by the bloody attack on the Sunni mosque a day before.
Salim al-Juburi called for political unity and said "the main aim [of the attack] is to foil all the efforts that have been made to form a government."
"All the political entities condemned the crime, all of them expressed their anger about what happened," he said in televised remarks.
"Now we are waiting for practical measures to hold the criminals accountable."
Iraqi premier-designate Haidar al-Abadi, a Shiite Arab, has condemned the attack and called for "citizens to close ranks to deny the opportunity to the enemies of Iraq who are trying to provoke strife."
Army and police officers said the attack on the Musab bin Omair Mosque in Diyala came after Shiite militiamen were killed in clashes, while other sources said it followed a roadside bomb near one of their patrols.
Doctors and the officers put the toll from the attack, in which worshippers were sprayed with machine-gun fire, at 70 dead and 20 wounded.
Two officers had earlier blamed ISIS for the attack, saying it had included a suicide bombing, a hallmark of the group, but most accounts pointed to Shiite militiamen.
The interior ministry announced it is conducting an investigation into the attack, which it said was carried out by two gunmen on a motorbike following a bombing targeting security and volunteer forces in the area.
The government turned to militiamen to bolster its flagging forces during the ISIS offensive, sparking a resurgence of groups involved in brutal sectarian killings in past years.
Ibrahim Aziz Ali, whose 25-year-old nephew was among those killed, told AFP he and other residents heard gunfire and rushed to the mosque, where they were fired on by snipers.
Five vehicles with images of Imam Hussein, one of the most revered figures in Shiite Islam, were parked at the mosque, Ali said.
When they could finally enter, "we found a massacre," he said.
Officers said that angry residents exchanged fire with security forces and militiamen in the area Friday, but reported no casualties.
US Vice President Joe Biden, writing in The Washington Post, said the US would back a system of "functioning federalism" in Iraq as a means to breach the divisions in the country, and that the US was prepared to "further enhance" its support for Iraq's fight against IS.
The United States began an air campaign against ISIS in Iraq on April 8, and has since carried out more than 90 strikes, including three against militants in the area of the Mosul dam, the country's largest, Friday.
Pentagon chiefs warned of the dangers of ISIS and said operations against it in Syria may also be needed.
"They marry ideology and a sophistication of strategic and tactical military prowess," US Defence Secretary Chuck Hagel. "This is beyond anything we have seen."
Foley's killing has stoked Western fears that territory seized by the militants in Syria and Iraq could become a launchpad for a new round of global terror attacks.
Foley, a 40-year-old freelance journalist, was kidnapped in northern Syria in November 2012.
In the execution video, released online, a black-clad militant said Foley was killed to avenge US air strikes against ISIS.
The man, speaking with a clear south London accent, paraded a second US reporter, Steven Sotloff, in front of the camera and said he too would die if Washington kept up its attacks.