ARBIL, Iraq (AFP) - US Secretary of State John Kerry heads to Cairo on Saturday, amid a growing campaign to build a broad international coalition for a "war" against the Islamic State in Syria and Iraq (ISIS).

Retired US general John Allen, the hawkish ex-commander of Nato forces in Afghanistan who also led troops in western Iraq, was named on Friday to lead the international effort against the extremists. Allen, 60, is on record saying that ISIS "is an entity beyond the pale of humanity and it must be eradicated. If we delay now, we will pay later."

Both the White House and the Pentagon stressed that the United States is now "at war" with the group that has seized large chunks of Iraq and Syria. But Kerry appeared reluctant to use the term in a series of television interviews, speaking instead of a "major counterterrorism operation" as Washington expands its campaign against ISIS.

"The United States is at war with ISIL in the same way that we are at war with Al-Qaeda and its Al-Qaeda affiliates all around the globe," White House spokesman Josh Earnest said, using another acronym by which the group is known.

Earlier Friday, French President Francois Hollande travelled to war-torn Iraq while Washington's top diplomat Kerry was in neighbouring Turkey, ramping up efforts to address what they now see as the global threat posed by the jihadists.

Hollande thus became the first head of state to visit Iraq since the militants seized large parts of the country in June, and he said France was ready to step up its military involvement.

The French leader is trying to take a lead role in responding to the crisis and will host a conference on Iraq in Paris on Monday.

'A broad-based coalition'

Kerry, speaking to reporters in Ankara, spoke of "a broad-based coalition with Arab nations, European nations, the United States and others."

Turkey is a fellow Nato member but has so far refused to open its air bases to US forces and other members of the coalition Washington is trying to put together against jihadists. He held a two-hour meeting with President Recep Tayyip Erdogan.

But a Turkish official told AFP that Ankara's hands were tied because of the fate of 49 Turks, including children and diplomats, kidnapped by militants in the northern Iraqi city of Mosul in June.

The previous day in Jeddah, Saudi Arabia, Kerry secured the backing of 10 Arab states for a global push to weaken ISIS, whose appeal has drawn volunteers from around the world.

In Cairo, Kerry will press his campaign to build a broad international coalition and will meet, among others, Arab League chief Nabil al-Arabi. However, Washington has insisted it will not work with Syrian strongman Bashar al-Assad and his regime.

The conflict in Syria has killed around 200,000 people in three and half years and allowed the emergence of the most violent and powerful group in modern jihad.

ISIS led a major offensive in Iraq that began on June 9 and swept through the country's Sunni Arab heartland, where many are angry and alienated by what they see as the sectarian policies of the Shiite-dominated government. ISIS declared a "caliphate" straddling both countries, attacked minorities, posted videos of beheadings online and vowed to take the fight to the West. That sparked what has been decried as a belated reaction from world powers, with US President Barack Obama this week outlining a strategy to stamp out the group.

Over 150 US strikes

The CIA put the number of fighters in IS ranks at 20,000 to 31,500 in Iraq and Syria, up to three times the previous estimate. US aircraft have carried out more than 150 strikes in Iraq since early August, the latest coming on Friday in the area of the country's largest dam, north of Mosul, in which two ISIS vehicles were destroyed, according to the US military.

Washington plans to help revamp the Iraqi army, which withered under the ISIS-led onslaught in June, and has announced it would fly combat aircraft from an airbase in the Kurdish regional capital Arbil.

Three years after the end of the nearly nine-year US military presence in Iraq, which some observers say birthed what is now ISIS, Obama has been careful to stress to the war-weary American public that he would not send ground forces into combat.

Efforts also focus on tackling what is considered the worst humanitarian crisis on the planet, which has created more three million Syrian refugees and displaced up to 1.8 million in Iraq, with the continued conflict taking a daily toll.

Hollande, who flew to Iraq with 15 tonnes of aid on his plane, stopped in Arbil to visit displaced Christians in a camp. France was quick to offer taking displaced Christians in, but Hollande said "the first duty we have is to fight against terrorism, it is not to give in to terrorism by drawing people" out of their homeland.

Germany, which has ruled out taking part in air strikes against IS, outlawed providing active support to IS, warning that the group poses a threat to Europe.