The US-led coalition widened its air strikes against the Islamic State group in Syria Saturday as British warplanes took off on anti-jihadist missions over neighbouring Iraq.

Seven targets were hit in Syria, the Pentagon said, including an IS building and two armed vehicles at the border crossing in the besieged Kurdish town of Ain al-Arab, also known as Kobane.

The Syrian Observatory for Human Rights monitoring group said IS rockets also hit the town, for the first time since the jihadist assault began on September 16, wounding 12 people.

The jihadist advance on the town has sent 160,000 refugees streaming into Turkey.

Other targets in Syria included IS vehicles and buildings near Al-Hasakeh, as well as an IS command and control facility near Minbej, US Central Command said.

Meanwhile, Royal Air Force Tornado GR4 combat jets armed with laser-guided bombs took off from Britain's RAF Akrotiri base on Cyprus for missions over Iraq but returned after seven hours without having used their weapons.

"On this occasion no targets were identified as requiring immediate air attack by our aircraft," a defence ministry spokesman in London said.

Belgium and Denmark have also approved plans to join France and the Netherlands in launching air raids against the militants in Iraq, allowing Washington to focus on the more complex operation in Syria, where IS is based.

Washington warned that the jihadists could not be defeated in Syria by air power alone, saying that up to 15,000 "moderate" rebels would need to be trained.

Saturday was the second time US-led air strikes had been reported around Ain al-Arab since the IS advance began.

- Turkey mulls 'necessary steps' -

President Recep Tayyip Erdogan said Saturday Turkey could take a military role in the coalition, the Hurriyet daily reported.

He said the government would go to parliament with a motion on October 2 and after this "all the necessary steps" would be taken for its involvement.

Ankara has for months frustrated the West with its low-key role in the anti-IS campaign but insisted its hands were tied because of dozens of Turkish hostages abducted by IS in Iraq, who are now free.

Hundreds of Syrian Kurdish refugees, clutching what possessions they could grab, crossed the border Saturday to safety inside Turkey, saying they were fleeing the renewed assault by IS.

Senior Syrian Kurdish official Newaf Khalil told AFP the latest strikes hit the IS-held town of Ali Shar, east of Ain al-Arab, and destroyed several IS tanks.

Saturday's strikes came a day after hundreds of Kurdish fighters crossed from Turkey to reinforce Ain al-Arab's Kurdish militia defenders.

Coalition aircraft also pounded the Euphrates valley city of Raqa, which the jihadists have made the headquarters of the "caliphate" they declared in June straddling swathes of Iraq and Syria.

"At least 31 explosions were heard in Raqa city and its surroundings," said the Britain-based Observatory.

Washington has been keen not to let Syrian President Bashar al-Assad's forces exploit the anti-IS air campaign to take the upper hand in the more than three-year-old civil war.

- 'Near continuous' combat sorties -

The US and Arab allies began air strikes against IS in northern and eastern Syria on Tuesday, more than a month after Washington launched its air campaign against the jihadists in Iraq.

Washington had been reluctant to intervene in Syria, but acted after the jihadists captured more territory and committed widespread atrocities, including beheading three Western hostages.

A US defence official told AFP Friday that the Syrian mission is now similar to US-led air raids against IS in Iraq, with "near continuous" combat sorties.

Washington is also planning to train and arm 5,000 Syrian rebels as part of the effort, although the top US military officer, General Martin Dempsey, said between 12,000 and 15,000 men would be required to recapture "lost territory" in Syria.

Dempsey said defeating IS would take more than air strikes and that "a ground component" was an important aspect of the US-led campaign.

"We believe the path to develop that is the Syrian moderate opposition," he said.

European governments have so far ruled out launching strikes in Syria, although Britain "reserved the right" to intervene there in case of an imminent "humanitarian catastrophe".

Washington has instead been supported in its Syria campaign by Arab allies Bahrain, Jordan, Qatar, Saudi Arabia and the United Arab Emirates.

Iran has warned that it too would attack the jihadists in Iraq if they advanced near the border.

"If the terrorist group (IS) come near our borders, we will attack deep into Iraqi territory and we will not allow it to approach our border," ground forces commander General Ahmad Reza Pourdestana told state media.

The Sunni extremists of IS control territory north of Baghdad, including in Diyala province bordering Shiite Iran.

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