Iraqi officials worked Saturday to ease soaring tensions after 70 people were gunned down at a Sunni mosque, as attacks in Baghdad and areas to its north killed over 30 more.

The attack at the mosque in Diyala province the day before, which most accounts said was the work of Shiite militiamen, threatens to increase anger among Iraq's Sunni Muslim minority with the Shiite-led government at a time when an anti-militant drive depends on their cooperation.

The violence came as the US, which is carrying out air strikes in Iraq against Islamic State (IS) jihadists, ramped up its rhetoric over the grisly killing of journalist James Foley by the group and shown in a video posted online.

Deputy National Security Adviser Ben Rhodes said Foley's beheading "represents a terrorist attack against our country".

On Saturday, Iraq's Sunni parliament speaker sought to calm sectarian tensions.

Salim al-Juburi called for political unity and said "the main aim (of the mosque 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."

- Call to close ranks -

Premier-designate Haidar al-Abadi, a Shiite, 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".

Rights group Amnesty International called Friday's attack a "massacre", and said Iraqi authorities "must properly investigate".

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 bombing near one of their patrols.

Doctors and the officers put the toll from the attack, in which worshippers were sprayed with machinegun fire, at 70 dead and 20 wounded.

Two officers earlier blamed IS for the attack, but most accounts pointed to Shiite militiamen.

The interior ministry announced an investigation into the attack, which it said was carried out by two men 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 an IS-led offensive that has overrun large areas of five provinces since June, but in doing so has encouraged a resurgence of groups involved in brutal sectarian killings in past years.

Ibrahim Aziz Ali, whose 25-year-old nephew was among those killed Friday, told AFP he saw five vehicles bearing images of Imam Hussein, one of the most revered figures in Shiite Islam, parked at the mosque.

When he and other residents could finally enter, "we found a massacre", Ali said.

- More violence -

As officials sought to limit the fallout from the mosque attack, more violence killed at least 34 people and wounded more than 150, officials said.

Three car bombs exploded in the northern city of Kirkuk, killing 21 people, while six more died when a suicide bomber detonated an explosives-rigged vehicle at the entrance to the interior ministry's intelligence headquarters in Baghdad.

The bodies of six soldiers killed Saturday, bearing bullet wounds and with hands bound, were left on a road south of the militant-held city of Tikrit, while a roadside bomb hit a vehicle carrying civilian volunteers north, killing one.

The United Nations, meanwhile, warned that the Shiite Turkmen-majority Iraqi town of Amerli is under threat of a "massacre" by jihadists who have besieged it for more than two months.

"The situation of the people in Amerli is desperate and demands immediate action to prevent the possible massacre of its citizens," UN Iraq envoy Nickolay Mladenov said in a statement.

Abadi and Iraq's top Shiite cleric, Grand Ayatollah Ali al-Sistani, both also called for efforts to help Amerli.

The United States launched an air campaign against IS in Iraq on April 8, and has since carried out more than 90 strikes, including one in the area of the Mosul Dam, the country's largest, on Saturday.

America's top military officer has said that anti-IS operations in Syria may also be needed.

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.

The 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 IS.

The man, speaking with a clear south London accent, paraded a second American reporter, Steven Sotloff, in front of the camera and said he too would die if Washington kept up its attacks.

US backs federal system in Iraq: Biden
Washington (AFP) Aug 23, 2014 - Vice President Joe Biden said Friday the United States would back a federal system in Iraq, as he pressed for unity in the sharply divided country amid a growing terror threat.

Writing in a Washington Post opinion piece, Biden said the United States was ready to "further enhance" its support of Iraq's fight against the Islamic State, and would urge its international partners to do so as well.

Biden warned that the deep sectarian divisions and political mistrust had "sapped the strength" of Iraqi security forces and strengthened militants like IS, which has seized a swath of the country and neighboring Syria.

He pointed to "functioning federalism" as an approach to breach the divisions in Iraq. Biden is a longtime supporter of the plan under which Iraq would be divided into three semi-autonomous regions for Shiites, Sunnis and Kurds, respectively.

A plan along these lines would "ensure equitable revenue-sharing for all provinces and establish locally rooted security structures, such as a national guard, to protect the population in cities and towns and deny space for ISIL while protecting Iraq's territorial integrity," Biden said, using another acronym by which IS is known.

"The United States would be prepared to offer training and other forms of assistance under our Strategic Framework Agreement to help such a model succeed," he added.

Biden called for "genuine compromise" from all sides in Iraq.

"We cannot want that more than Iraqis do," the US vice president said.

"Unless Iraq can do this, no amount of outside intervention will matter -- nor will it continue indefinitely."

Despite a US campaign of air raids backing regional Kurdish and Iraqi forces fighting IS in the north of the country, he insisted the threat "can be routed by local forces without US boots on the ground."

"This is a fight that Iraq, with help from America and the world, can and must win," Biden said, speaking of a "long-term challenge."

"We all have a stake in empowering moderates in Iraq to prevent a terrorist state from taking root in the heart of the Middle East."

He acknowledged that "the threat, of course, is not confined to Iraq," calling for continued support from regional powers and the Syrian opposition to counter IS and the flow of foreign fighters to and from the battlefield.

"This is a fight that Iraq, with help from America and the world, can and must win," Biden said.