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 (six kilometers) from Bab al-Hawa, said Assad Kanjo, an anti-Assad
activist based in the province.

Over the past week the al-Qaida-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-Qaida breakaway
group calling itself the Islamic State as well as Assad’s forces.

But when the U.S.-led coalition began launching airstrikes against the Islamic State group 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.

The Islamic State group 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 the Islamic State group and the Nusra Front — bitter ideological rivals
who have repeatedly battled one another — are acting in unison.