Obama toughens stand, vows to expand air strikes over Syria

US President Barack Obama announced on Wednesday night he was expanding the US air campaign against the Islamic State to enter Syria, promising to "degrade and ultimately destroy the terrorist group".

Obama said that after three years of trying to keep America out of Syria's civil war he had decided to ramp up the supply of weapons to the moderate Syrian rebels and train them to fight both the Islamic State and the Assad regime.

Speaking from the White House, the President ruled out cooperating with the Assad regime against ISIL, saying Syria's Shia government could never "regain the legitimacy it has lost" by killing thousands of the country's Sunnis.

Obama also announced he was expanding American airstrikes in Iraq, giving US fighter pilots freer rein to strike ISIL targets across the country and cover Iraqi ground troops as they "go on offense".

He also ordered a further 475 US troops to Iraq to advise the country's military and support the air mission, bringing the total American force inside Iraq to around 1,500.

The President promised a war-weary American public that their country would not act alone but had the support of allies in both the West and the Middle East.

"America will lead a broad coalition to roll back this terrorist threat," Obama said. "We will degrade, and ultimately destroy, ISIL through a comprehensive and sustained counter-terrorism strategy."

He also vowed that American troops "will not get dragged into another ground war" and compared the campaign against ISIL to other US counter-terror missions in Yemen and Somalia.

Obama spoke for less than 15 minutes during the prime-time peak television viewing hour in a speech intended to rally support among the American people.

According to a recent CNN survey, public opinion has been galvanised by the murder of two American journalists and 76 per cent support additional strikes against ISIL.

Speaking on the eve of the anniversary of the 11 September attacks, Obama said US intelligence had "not yet detected specific plotting against our homeland" but he had decided that "if left unchecked" ISIL could eventually attack America.

"I have made it clear that we will hunt down terrorists who threaten our country, wherever they are. That means I will not hesitate to take action against ISIL in Syria, as well as Iraq," he said.

The President reiterated fears that foreign fighters with US or European passports could return to commit attacks in their home countries and promised to chair a special meeting of the UN Security Council to discuss the threat they posed.

White House aides said the US had secured a commitment from Saudi Arabia to host training camps for the Syrian rebels. "We now have the commitment from the Kingdom of Saudi Arabia to be a full partner in this effort," one said.

John Kerry, is in Saudi Arabia today to discuss cooperation against the jihadists.

Obama has long been reluctant to intervene significantly into Syria's civil war by arming the rebels, overruling Hillary Clinton and other aides who urged more aggressive action.

But, on Wednesday night, he described the rebels as "the best counterweight to extremists like ISIL" and promised to pursue what he called "the political solution necessary to solve Syria's crisis once and for all".

The President did not say whether the US would strike the Syrian government's sophisticated air defence systems in order to ensure American aircraft could fly unimpeded over Syria.

His aides insisted that attacking ISIL would not strengthen the Assad regime on the battlefield, saying the Sunni areas under jihadist control would never accept being ruled by the Shia government in Damascus.

A US military official suggested that strikes against Syria could be some time off, saying, "Decisions about when to conduct these actions will be made at a prudent time."

US surveillance aircraft are currently carrying out missions over Syria to compile lists of targets and gather intelligence on the location of ISIL leaders.