Iraq has welcomed US President Barack Obama's plan for an international coalition against jihadists as a "strong message of support", after repeatedly calling for aid against the militants.

Obama outlined the plan at a NATO summit on Friday, calling for a broad coalition to defeat the Islamic State (IS) jihadist group which led an offensive that overran chunks of five Iraqi provinces in June and holds significant territory in neighbouring Syria.

International concern has been building over IS, which has carried out numerous atrocities including killings, kidnappings and attacks on minorities in areas it controls in the two Arab states.

But the beheading of American journalists James Foley and Steven Sotloff, which IS claimed, have sparked significantly more outrage in the West than its other abuses, providing increased impetus for action.

On Saturday, the United Nations Security Council added further pressure, condemning the "heinous and cowardly" murder of Sotloff and saying that IS "must be defeated".

The United States has sent military advisers to Iraq and launched a campaign of air strikes against the jihadists, while it and a string of other countries have promised arms for Iraqi Kurdish forces battling IS militants.

It carried out two more strikes on Friday and Saturday with a "mix of attack, fighter and remotely piloted aircraft," the US military's Central Command said in a statement.

The strikes destroyed four Humvees, one armoured personnel carrier and two trucks belonging to IS fighters, according to CENTCOM.

The American strikes raised to 133 the total carried out across Iraq since August 8, at least some of which, such as attacks on Humvees, are destroying US military equipment which the jihadists captured from the Iraqi military.

Obama said regional involvement was "absolutely critical" for the anti-IS effort, although the State Department added there were "no plans" for military coordination with Iran in the fight.

"We're going to degrade and ultimately defeat (IS)," Obama said.

He said there was "unanimity" among NATO members that the group "poses a significant threat", but European allies of the United States, while supportive of Obama's initiative, were more cautious.

Iraqi Foreign Minister Hoshyar Zebari praised Obama's remarks as a strong response to Baghdad's long-standing appeals for aid.

"We welcome that, and we have repeatedly called on our international partners for help and support because this threat is a very deadly threat... not only to the people of Iraq or the region, but to Europe, to America, to NATO," Zebari told AFP on Saturday.

"This is basically our fight ... but we need the support -- our capacity is limited, and we need the support to enhance our capacity.

"Nobody's thinking of any ground troops at this stage -- they are calling for air support, for tactical support, for arming the forces on the ground, like the (Kurdish) peshmerga, the Iraqi security forces, and also to provide... intelligence, reconnaissance," said Zebari.

Across the border on Saturday, Syrian air strikes in the jihadist-held northern city of Raqa killed 53 people, including 15 jihadists and at least 31 civilians, the Syrian Observatory for Human Rights said.

The targets on Saturday included a building housing an IS Islamic court and a training camp. Twenty-four of the dead were killed when a bakery was hit.

Washington has said operations in Syria will be needed to defeat IS, but has thus far ruled out any co-operation with the government in Damascus.