Al Nusra Front are battle-hardened jihadists who have been winning battle after battle against the Syrian army and will most likely wipe the floor with non-jihadist FSA units.

TAL ABYAD, Syria — Two Syrian rebel groups – one seeking an elected civil government, the other favoring the establishment of a religious state – are battling each other in the city of Tal Abyad, on the border with Turkey, in a sign of the tensions that are likely to rule this country if the government of President Bashar Assad falls.

Four people were killed Sunday in fighting here between the Farouq Battalions, which favors elections, and Jabhat al Nusra, or the Nusra Front, which the United States has declared an al Qaida-affiliated terrorist group. Since then, Farouq has been massing men here in an example of the growing friction that’s emerged in recent months as Nusra has captured strategic infrastructure across Syria’s north and east, including oil and gas installations, grain silos and a hydroelectric dam.

Raqqa province, where Tal Abyad is, and Hasaka province, to the east, are poverty-stricken but vital to Syria’s agriculture. Hasaka and Deir el Zour province to the south are the center of the country’s oil industry.

“They want to control the border crossing here,” said Abu Mansour, a member of Farouq in Tal Abyad. Like other rebels, he uses a nom de guerre to hide his identity from the government.

The rivalry between the groups is a reminder of how divided Syria’s rebel factions are and how inaccurate it is to refer to the anti-Assad forces as if they were a single group, with a single goal. Indeed, while news stories for months often referred to rebels as the Free Syrian Army, that term is more an idea than an organization. Instead, the rebel movement comprises dozens of groups whose ideologies have only one common goal: the toppling of the Assad regime.

Farouq, which has battalions across Syria and espouses a moderate interpretation of Islam, controls border crossings with Turkey at Tal Abyad and Bab al Hawa, in northwestern Syria. Nusra has attempted to seize control of both crossing points since Farouq took them from pro-Assad forces last September.

The rivalry between the groups has become increasingly apparent as Nusra raises the volume of its calls for Islamic law. Recently, it suggested it might declare Raqqa, the largest city under rebel control, the center of an Islamic emirate. Last November, the group clashed with members of Kurdish militias after it seized the border crossing at Ras al Ayn.