US President Barack Obama has overhauled Washington's approach to supporting Syrian rebel forces following this year's deeply troubled launch of a US military training programme.

Defence Secretary Ash Carter said the new approach would focus more on enabling forces already on the ground to battle Islamic State (IS). The original US military effort sought to train entire units outside Syria, at sites in Turkey and Jordan, and then send them back into the civil war.

Speaking in London after talks with his British opposite number Michael Fallon, Mr Carter said: "We have devised a number of different approaches."

In May, the US military began training for up to 5,400 fighters a year in what was seen as a test of Mr Obama's strategy of having local partners combat IS and keep US troops off the front lines.

But the programme was troubled from the start, with some of the first class of fewer than 60 fighters coming under attack from al Qaeda's Syria wing, Nusra Front, in their battlefield debut.

Mr Carter said the new US effort would seek to enable Syrian rebels in much the way the US had helped Kurdish forces to successfully battle Islamic State in Syria.

"The work we've done with the Kurds in northern Syria is an example of an effective approach where you have a group that is capable, motivated on the ground, that you can enable their success," Mr Carter said.

"That's exactly the kind of example that we would like to pursue with other groups in other parts of Syria going forward. That is going to be the core of the President's concept."

A senior US defence official, speaking to reporters travelling with Mr Carter, said the programme itself was not ending, adding there would be some training and vetting of Syrian rebels in the future.

But the overhaul would clearly turn a new page on what had been a failed experiment for the US military.

In the face of its brutal offensive through northern Iraq in June, 2014, Mr Obama asked Congress for an initial $500 million to "train and equip" Syria's opposition fighters, whom he later described as "the best counterweight" to Islamic militants and a key pillar in his campaign to defeat them.

The plan reflected the priorities of a president reluctant to get entrenched in another Middle East conflict, but who needed a ground force to complement US airstrikes against IS in Syria.

The US military programme also failed to attract enough recruits, with many candidates being declared ineligible and some even dropping out.