The US has bombed Islamic State (Isis) fighters near the Iraqi capital of Baghdad as its expanded operation against the extremist group begins.
Barack Obama vowed to “degrade and destroy” Isis following the beheading of two American journalists and its bloody rampage through Syria and Iraq.
US intervention has been welcomed by international allies that backed a resolution on Monday to use military action “if necessary” in the fight against Isis.
But it was condemned by Iran as a ruse to “dominate” the Middle East from a country with “corrupted hands”.
The US Central Command said it conducted two air strikes on Sunday and Monday in support of Iraqi forces being attacked by enemy fighters near Sinjar and south-west of Baghdad.
Six Isis vehicles and one of the group's fighting positions that was firing on the Iraqis were destroyed, a spokesperson said.
It marks a shift in American military policy in Iraq, where forces have only worked primarily to protect “US interests” and personnel, and in humanitarian efforts since strikes were first authorised in August.
President Obama said they were necessary then to prevent “genocide” being carried out by Isis as 40,000 civilians from the Yazidi religious minority were trapped without food or water on Mount Sinjar.
US forces bombed Isis to ensure the safe passage of refugees of the mountain and to protect workers doing aid drops.
But the latest bombing is in direct support of Iraqi forces fighting the militants, at the request of the national Government.
The foreign ministers of more than 20 countries, including Britain, the US, Saudi Arabia and the United Arab Emirates, backed a pledge on Monday to fight Isis using “any means necessary”, including military action.
Philip Hammond, the Foreign Secretary, said the UK would play a “leading role” in the coalition but did not specify what it will involve.
Air strikes have not been ruled out but the Prime Minister has repeatedly said ground troops will not be deployed.
Monday’s summit in Paris came little over a day after the murder of aid worker David Haines, who was shown being beheaded by a British Isis militant who went on to threaten the life of hostage Alan Henning, a charity worker from Salford.
Video: The death of David Haines - London Live
The only country to publicly decline an invitation to the conference was Iran, where the Supreme Leader Ayatollah Ali Khamenei said he refused American requests for help because the country “had dirty hands”.
A stream of tweets were later sent from his official account lambasting America’s record in the Middle East and claiming attacks on Isis were a ruse to “dominate the region”.
“US officials’ remarks on creating a coalition in the name of fighting Isis is empty, shallow and biased,” he said.
“US goal in planning a war on Isis is to dominate the region and turn Iraq and Syria to Pakistan where it can commit crimes whenever it wants.
“If the US enters Iraq and Syria without permission, they will go through the same problems as they did over the past 10 years in Iraq.”
Additional reporting by PAReuse content