Clashes between Arab rebels and Kurdish militants in northeastern Syria are bringing additional complexities to the already murky front lines in the country’s civil war.

The latest round of fighting was prompted when two Sunni Arab rebel groups with reputed links to al-Qaeda captured a border crossing with Turkey in the Syrian town of Ras al-Ayn this month. The groups succeeded in driving out forces loyal to Syrian President Bashar al-Assad but also drew the ire of a Kurdish militia with a presence in the area. Dozens of Arabs and Kurds have been killed in the fighting that followed.

Analysts fear that the clashes could hamper efforts to unify Syria’s disparate opposition factions, deepen ethnic divisions and empower radical elements among both the Arabs and the Kurds.

Despite a cease-fire, the situation in Ras al-Ayn remained locked this week in a tense standoff between the two Arab groups — Ghuraba al-Sham and Jabhat al-Nusra — and the Kurdish Syrian Democratic Union Party, which is known by the acronym PYD.

More moderate rebel factions have criticized the two Islamist Arab groups for their decision to attack Ras al-Ayn without permission from the rebels’ military council, which is attempting to centralize decision making.

(Gene Thorp/The Washington Post)

The attack inflamed already tense relations between the majority Arab opposition and Syria’s Kurds. It also underscored the determination of more-
radical elements within the opposition to buck the will of those attempting to unify the rebellion against Assad.

The fighting in Ras al-Ayn is not the first time that Arab forces have clashed with Kurds, who compose about 10 percent of the country’s population. Last month, battles occurred in the northern city of Aleppo after Arab rebels entered a Kurdish neighborhood. But the fighting in Ras al-Ayn is the first time that Arab rebels have attacked so far east in territory largely controlled by the PYD.

“There are a lot of efforts to limit the extremist groups in Aleppo province,” said Andrew J. Tabler, a Syria expert at the Washington Institute for Near East Policy. “I think they are looking for a safe haven and a place where they can find some opportunities to carry out attacks against the regime forces. That takes them dangerously close to Kurdish areas.”

The PYD, meanwhile, has expanded its area of influence by using a past relationship with Assad’s government to broaden its footprint as regime forces have been transferred to other areas.

“They struck a deal of sorts with the regime that gave them some room in the north of the country,” said Peter Harling, an expert on Syria with the International Crisis Group.

That expansion is seen as part of the PYD’s long-standing efforts to achieve autonomy — and perhaps independence.

Having fought a decades-long war with Kurdish militants affiliated with the PYD, Turkey has expressed deep concern about PYD forces massing along its southern border.

Syria’s 20-month-old conflict arrived in Ras al-Ayn, a border town consisting of Arabs, Kurds and a small Christian population, early this month. The Syrian Observatory for Human Rights, which monitors the conflict, reported that rebels entered the town from Turkey and from a Syrian village to the west.

After the Arab rebels drove regime forces from the town and seized control of the border crossing, PYD forces withdrew into the eastern Kurdish parts of the town “in order to show good intention and that we were not against the uprising,” said Nasser Haj Mansour, a PYD spokesman.

However, clashes began after an incident at a PYD checkpoint, with both sides demanding that the other leave Ras al-Ayn and neither complying.

Various Kurdish groups have met in Irbil, the capital of neighboring Iraqi Kurdistan, and have attempted to form a united opposition to the Arab forces. “Reinforcements are coming,” Mansour said. “Until now, we did not attack them. We just defended ourselves.”

But Harling said he doubted that either side had an interest in a major escalation. “It would be a distraction from other objectives,” he said.