By John Irish and Jason Szep

PARIS (Reuters) – French President Francois Hollande called on Monday for united international action to tackle the threat from Islamic State militants as he opened a conference on Iraq bringing together members of a U.S.-led coalition.

The United States this week unveiled an outline plan to fight the Islamist militants simultaneously in Iraq and Syria. It believes it can forge a solid alliance despite hesitancy among some partners and questions over the legality of action, notably in Syria where the militant group has a power base.

“What is the threat?” the French leader said as he opened the one-day meeting of officials from some 30 states in Paris.

“It is global so the response must be global … Iraq’s fight against the terrorists is also our fight. We must commit ourselves together – that is the purpose of this conference,” said Hollande, who last week traveled to Baghdad to meet members of Iraq’s new government.

Iraqi President Fuad Masum said he hoped the Paris meeting would bring a “quick response” to jihadists who have declared a caliphate or Islamic state ruled under Sharia law in the heart of the Middle East.

“Islamic State’s doctrine is either you support us or kill us‎. It has committed massacres and genocidal crimes and ethnic purification,” he told delegates.

Foreign ministers from the main European states, the five permanent members of the U.N. Security Council, Iraq’s neighbors and Gulf Arab states Qatar, Saudi Arabia, Kuwait and the UAE, gathered to discuss political, security and humanitarian aspects of tackling Islamic State.

Iran, which is highly influential in its neighbor Iraq, is not attending the conference.

“We wanted a consensus among countries over Iran’s attendance, but in the end it was more important to have certain Arab states than Iran,” a French diplomat said, signaling that Saudi Arabia had not been keen on Tehran coming.

French officials say the coalition plan must go beyond military and humanitarian action, arguing there must also be a political plan for once Islamic State has been weakened in Iraq.

They argue that the 2003 US-led intervention in Iraq, in which Paris did not participate, ultimately contributed to the current crisis because it lacked a long-term vision for the different strands of Iraqi society.