Thirty countries have pledged to help Iraq fight Islamic State (IS) militants “by all means necessary”.
A joint statement by foreign ministers taking part in a major conference in Paris talks said support would include “appropriate military assistance”.
The talks had been called to agree a strategy to combat the group, which controls large parts of Iraq and Syria.
The conference followed a whirlwind tour of the Middle East by US Secretary of State John Kerry.
Mr Kerry, who attended the summit, has been drumming up support for a plan of action unveiled by President Barack Obama last week.
The murder of British aid worker David Haines by IS militants, shown in a video released by the group on Saturday, has added momentum to the plans, says the BBC’s Lucy Williamson in Paris.
Opening the summit, French President Francois Hollande said the threat posed by IS militants needed a global response.
The CIA estimates that Islamic State – formerly known as ISIS – has between 20,000 and 31,000 fighters in Iraq and Syria.
Iraqi President Fuad Masum, who co-hosted the conference with Mr Hollande, said the international community must pursue the jihadists “quickly”.
“If this intervention and support to Iraq is late, that means that Islamic State could occupy more territory and the threat it poses will be even bigger,” he said.
The summit closed a few hours later with a joint statement saying the participants were “committed to supporting the new Iraqi government in its fight… by any means necessary, including appropriate military assistance”.
Earlier, France said it had begun surveillance flights over Iraq. Britain revealed in August that its aircraft had been gathering intelligence over Iraq.
Several Arab countries have offered to take part in air strikes on IS fighters in Iraq, US officials say.
Turkey, however, will only allow humanitarian and logistical operations from the Nato air base on its soil.
Mr Kerry said he was “extremely encouraged” by promises of military assistance to tackle the militant group.
Analysis: Barbara Plett-Usher, BBC News
Mr Kerry has declared his coalition-building efforts in the Middle East a success, saying he won “full-throated” support from Sunni governments in the region for America’s campaign against Islamic State [Sunni] militants who have taken over one third of Syria and Iraq.
But few specifics have been presented to flesh out this upbeat assessment in the scramble to craft a coherent plan from contributions offered by at least 40 countries worldwide in time for the UN General Assembly next week.
The cornerstone of the trip was a communique signed in Jeddah by 10 Arab governments agreeing to “do their share” in the comprehensive fight against Islamic State, including participation in a co-ordinated military campaign.
The military details, at least, seem to be falling into place.
Daunting task ahead for US-led coalition
The US strategy to weaken the group centres on military support for Iraq but also includes plans to stop foreign fighters from joining the group, cutting its funding streams and trying to counter its ideology.
The Paris conference was aimed at defining the role each member state will play.
About 40 countries have so far signed up to a coalition including 10 Arab states – Egypt, Iraq, Jordan, Lebanon, Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates.
Neither Iran nor Syria are being allowed to take part.
Last week Mr Kerry ruled out co-operation with Iran citing its “engagement in Syria and elsewhere”.
But Iranian Supreme Leader Ayatollah Ali Khamenei claimed on Monday that the US had requested Iran’s co-operation via the US Ambassador to Iraq.
“I said no, because they have dirty hands,” he said.
He added the US was seeking seeking a “pretext to do in Iraq and Syria what it already does in Pakistan — bomb anywhere without authorisation”.
Australia announced at the weekend that it was sending 600 troops and up to eight fighter jets to the UAE ahead of possible combat operations in Iraq.
However, Mr Kerry told US broadcaster CBS that the US was not seeking troops on the ground at the moment.
Since August, US fighter jets have conducted about 160 air strikes on IS positions in Iraq.