US to defend Syrian rebels with airpower, including from Assad

The decision by President Barack Obama, which could deepen the US role in Syria's conflict, aims to shield a still-fledging group of Syrian fighters armed and trained by the United States to battle Islamic State militants - not forces loyal to Assad.

But in Syria's civil war, Islamic State is only one of the threats to the US recruits. The first batch of US-trained forces deployed to northern Syria came under fire on July 31 from other militants, triggering the first known US airstrikes to support them.

US officials, speaking on condition of anonymity to confirm details of the decision, first reported by the Wall Street Journal, said the United States would provide offensive strikes to support advances against Islamic State targets.

The United States would also provide defensive support to repel any attackers. US officials have long played down the idea that Assad's forces - which have not fired on US-led coalition aircraft bombing Islamic State targets in Syria - would turn their sights on the US-backed Syrian rebels. But they cannot rule out the possibility, perhaps in an unintentional clash.

White House National Security Council spokesman Alistair Baskey said only the US-trained forces were being provided a wide range of support, including "defensive fires support to protect them" and pointed to July 31's US airstrikes as proof.

Pentagon spokeswoman Commander Elissa Smith also declined comment on the rules of engagement, saying only that the US military's program focuses "first and foremost" on combating Islamic State militants.

The US military launched its program in May to train up to 5,400 fighters a year in what was seen as a test of Obama's strategy of getting local partners to combat extremists and keep US troops off the front lines.