France's Hollande in Iraq to support new government

French President Francois Hollande arrived in Iraq Friday to support the new government, in the first visit by a head of state since militants overran large parts of the country three months ago.

Hollande's plane was carrying 15 tonnes of humanitarian aid to be delivered in the Kurdish capital of Erbil later Friday, after talks in Baghdad with his counterpart Fuad Masum, Speaker Salim al-Juburi and Prime Minister Haidar al-Abadi.

Meanwhile, the United States tripled its estimate for the number of Islamic State (IS) fighters as it geared up for a "more aggressive" air campaign and Arab nations rallied behind President Barack Obama's nascent coalition.

France has said it is prepared to participate in air strikes against the militants in Iraq "if necessary", and hosts an international conference on Iraq on September 15.

Ten Arab states including Saudi Arabia "agreed to do their share in the comprehensive fight" against IS, said a statement after a meeting Thursday between US Secretary of State John Kerry and his Arab counterparts.

The militants now have about 20,000 to 31,500 fighters on the ground in Iraq and Syria, the Central Intelligence Agency said, much higher than a previous estimate of 10,000.

"This new total reflects an increase in members because of stronger recruitment since June following battlefield successes and the declaration of a caliphate, greater battlefield activity, and additional intelligence," CIA spokesman Ryan Trapani said.

The vastly higher estimate underscored the scale of the challenge after Obama vowed to expand an offensive against the militants, a plan which foresees new air strikes against IS in Syria, expanded attacks in Iraq and new support for Iraqi government forces.

Iraq's new government and the Syrian opposition National Coalition welcomed Obama's plan against IS. But Syrian President Bashar al-Assad's government and powerful ally Russia condemned it.

"Any action of any kind without the consent of the Syrian government would be an attack on Syria," National Reconciliation Minister Ali Haidar said.

A Russian foreign ministry spokesman said unilateral action would be a "crude violation" of international law.

Kerry retorted that he was "really rather surprised that Russia would dare to assert any notion of international law after what has happened in Crimea and eastern Ukraine".

Republican doubts about Obama plan

Obama said he was sending another 475 military personnel to help train Iraqi forces, but stressed that the campaign would not be a repeat of the exhausting ground wars fought by US troops in the past decade in Iraq and Afghanistan.

Instead, Washington is looking to empower partners on the ground such as Iraqi and Kurdish forces, as well as Syrian rebels.

US combat aircraft will soon start flying out of a base in the Kurdish region of Iraq as part of the campaign, the Pentagon announced.

"The kind of support we're going to be giving to Iraqi forces will be more aggressive from the air," said Pentagon spokesman Rear Admiral John Kirby.

Obama called on Congress to swiftly authorise an operation to train and equip moderate fighters, but several House Republicans said after a caucus meeting Thursday that a quick vote on that was unlikely.

House Speaker John Boehner said they were worried that the broader strategy was insufficient.

"If our goal is to eliminate ISIL, there's a lot of doubt whether the plan that was outlined by the president... is enough to accomplish that mission," he said.

Along with the Saudis, Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates, as well as Egypt, Iraq, Jordan and Lebanon are Arab parties to the coalition agreement.

A final statement declared a "shared commitment to stand united against the threat posed by all terrorism, including the so-called Islamic State in Iraq and the Levant".

The fight will include "stopping the flow of foreign fighters through neighbouring countries, countering financing of ISIL and other violent extremists, repudiating their hateful ideology, ending impunity and bringing perpetrators to justice".

It will also include humanitarian relief, aiding reconstruction and rehabilitation of communities "brutalised by ISIL".

On Friday Kerry heads to Ankara after Turkey refused to allow its air bases to be used in the campaign or to take part in combat.

A US official in Jeddah said Turkey had its reasons for staying out of the coalition. IS militants hold 49 Turks hostage, including diplomats and children, abducted from the Turkish consulate in Mosul in Iraq in June.