Obama pledges Syria air strikes to eliminate Islamic State

US President Barack Obama on Wednesday ordered a "relentless" war against the Islamic State, including air strikes in Syria and expanded operations in Iraq to "destroy" the militants.

Obama - who hoped to go down in history for ending wars, not starting an open-ended escalation in the Middle East - also pledged to bolster Iraqi forces and increase military assistance to Syria's opposition.

In a prime-time televised address, Obama said the Islamic State, was a uniquely brutal group even by the blood-soaked standards of the Middle East.

"They execute captured prisoners. They kill children. They enslave, rape and force women into marriage," he said.

Such barbarity could bring only one response, Obama said.

"Our objective is clear: we will degrade, and ultimately destroy, [Islamic State] through a comprehensive and sustained counter-terrorism strategy," Obama said.

"I will not hesitate to take action against [Islamic State] in Syria, as well as Iraq," he said, using an alternative acronym for the self-declared Islamic State.

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

Despite previously hesitating to expand operations into Syria - out of fear that attacking IS there would benefit President Bashar al-Assad embroiled in a bloody three-and-a-half-year uprising against his rule – Obama’s words indicate that the battle against IS will now be brought across the border.

The A senior US official left no doubt that Obama's words represented an order for military operations in Syria, despite his long-held reluctance to get embroiled in the country's civil war.

"There will be action in Syria," the official told AFP, but declined to say when the first strikes would take place. "We are not going to telegraph our punches."

A senior defense official added: "The US military is ready to conduct direct action against [Islamic State] targets in Syria."

Syria's opposition National Coalition welcomed a US plan to tackle the jihadist Islamic State group on Thursday, but also urged action against President Assad.

In a statement, the group said it backed a US plan for air strikes in Syria and training of rebel forces, but that a "stable and extremist-free region" required "degrading and ultimately removing the Assad repressive regime."

The Syrian Coalition said it had "long called for this action, and... warned time and again of the growing threat of this extremist group."

"We urge the US Congress to approve the president's policy as soon as possible, and allow the training and equipping of the Free Syrian Army," it said.

The moderate Free Syrian Army "can succeed, but it needs the necessary support that would enable it to form a reliable and well-equipped force," the statement added.

It warned however that it was key to "realise that the Assad regime represents the root cause of the violence, brutality and sense of impunity prevailing in Syria."

Combating the Islamic State "alone cannot bring about a stable and extremist-free region," the group said.

Neither Iraq, nor Afghanistan

The extent of the campaign, however, remains unclear with Obama also seeking to preserve his doctrine of replacing wars and invasions with smaller more high-tech operations such as drone strikes.

Obama compared the new conflict to anti-terror operations in Somalia and Yemen.

And he made clear in the 14-minute address that the new front against terrorism will not become a repeat of the exhausting ground wars of the last decade.

"I want the American people to understand how this effort will be different from the wars in Iraq and Afghanistan," Obama said.

"It will not involve American combat troops fighting on foreign soil."

Instead, Washington will empower local partners like the Iraqi forces, Kurdish fighters and Syrian rebels, to fill in territory opened up by US air power, he explained.