The US and its “partners” have launched a barrage of bombs and Tomahawk cruise missiles on Islamic State extremists in Syria.

US media reported five Arab states took part in the air raids as part of a new international coalition formed to attack the Islamic State group, which has seized swathes of territory in Syria and Iraq.

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The US-led air assault in Syria marked a turning point in the war against the IS group, which Western governments fear could eventually stage terror attacks in Europe or the United States.

“I can confirm that US military and partner nation forces are undertaking military action against ISIL (Islamic State group) terrorists in Syria using a mix of fighter, bomber and Tomahawk Land Attack Missiles,” Pentagon spokesman Rear Admiral John Kirby said in a statement.

KILIS, Turkey – Syrians continue to walk on Sept. 10, 2014, seeking to illegally cross the border into an area near the southern Turkey city of Kilis from Syria before U.S. air strikes against Islamic State militants in their country. Photo: AAP

The decision to conduct the air strikes was undertaken earlier on Monday by the head of US Central Command, General Lloyd Austin, “under authorisation granted him by the commander in chief”, Kirby said.

“We will provide more details later as operationally appropriate.”

The strikes focused on IS positions in Raqa, a stronghold for the Sunni extremists, according to the New York Times, citing US officials. Other targets struck were along the Iraq-Syria border, the newspaper said.

The strikes – including Tomahawk missiles fired from naval warships at sea – came less than two weeks after Obama warned that he had approved an expansion of the campaign against the Islamic State group to include action in Syria.

“I have made it clear that we will hunt down terrorists who threaten our country, wherever they are,” Obama said on September 10 in a speech to the nation.

“This is a core principle of my presidency: if you threaten America, you will find no safe haven.”

Washington began air strikes against IS targets in Iraq on August 8, with about 190 raids carried out against the extremists there.

Obama has however repeatedly insisted the campaign would not involve a combat mission for US ground troops

Last week, the US Congress passed Obama’s plan to train and arm moderate Syrian rebels to battle the IS militants – part of his strategy to smash the movement that has beheaded two American journalists, James Foley and Steven Sotloff.

Lawmakers wary of triggering another war in the Middle East have vowed to hold broad use-of-force debates later this year following the November 4 midterm elections.

The air strikes in Syria came as Kurdish militia fought to defend a key border town in northern Syria, after 130,000 terrified residents fled to Turkey to escape an advance by the IS militants.

France is the only country to have joined the US air strikes against the IS in Iraq, where it emerged on Monday that the jihadists attacked an army base west of Baghdad with six suicide bombers at the weekend, killing 40 soldiers and capturing at least 70.

Australian special forces and RAAF members are in the United Arab Emirates but are not understood to be involved in the raids on Syria.