Syrian al Qaeda fighters massing near Turkish border

BEIRUT - Al Qaeda fighters are massing at a Syrian town on the Turkish border in what appears to be an attempt to seize a vital crossing from rebels, activists said on Monday.

If the Nusra Front seizes the Bab al-Hawa crossing, they will control a key supply line to the Syrian rebels, dealing another blow to U.S. plans to build up a moderate rebel force capable of fighting both Islamic extremists and President Bashar Assad's forces.

Nusra Front fighters have been gathering for the past few days in the town of Sarmada in the northern Idlib province, some four miles from Bab al-Hawa, said Assad Kanjo, an anti-Assad activist based in the province.

Over the past week the al Qaeda-linked fighters have wrested towns and villages from the Western-backed Syrian Revolutionary Front as well as other rebel groups, whittling down one of the last areas of northern Syria controlled by mainstream fighters.

Rami Abdurrahman of the Britain-based Syrian Observatory for Human Rights confirmed that Nusra fighters were gathering in the area but said there was no indication yet that they had advanced on the crossing.

The crossing is held by a rebel alliance known as the Islamic Front, and it is an important supply route for Western-backed fighters as well as aid groups that use the crossing to bring in food and medical supplies.

The Nusra Front had for months fought alongside Western-backed rebels against both the al Qaeda breakaway group calling itself the Islamic State of Iraq and Syria (ISIS) as well as Assad's forces.

But when the U.S.-led coalition began launching airstrikes against ISIS in late September it also struck the Nusra Front, angering moderate rebels. Those strikes may have driven a wedge between the two groups, leading the Nusra Front to view U.S.-backed rebels as a potential threat.

ISIS has been trying to seize the eastern border town of Kobani from Kurdish fighters for more than a month, hoping to expand its vast self-styled caliphate, which sprawls across a third of Syria and much of northern Iraq.

But there is no evidence that ISIS and the Nusra Front -- bitter ideological rivals who have repeatedly battled one another -- are acting in unison.