Militants in a rebel-held area of northern Syria have kidnapped two archbishops traveling from the Turkish border back to the city of Aleppo.

The kidnapping was reported by Syrian state media and confirmed by a member of the official opposition leadership, the BBC reported.

Yohanna Ibrahim is head of the Syriac Orthodox Church in Aleppo and Boulos Yaziji leads the Greek Orthodox Church in the city. They are the most senior Christian clerics caught up directly in the war.

It was not immediately clear who had kidnapped them.

Christians made up about 10 percent of the mainly Sunni Muslim country's population before the uprising against President Bashar al-Assad began two years ago. Many have sided with Assad, fearing their fate under Sunni rule.

State TV announced that an "armed terrorist group" -- which is what it calls all rebel forces -- had kidnapped the two bishops as they carried out "humanitarian work in Aleppo countryside."

Abdulahad Steifo, a Syriac member of the opposition Syrian National Coalition, said the men were seized on the road to Aleppo from the rebel-held Bab al-Hawa border crossing, which is close to the Turkish town of Reyhanli.

Asked who was behind their abduction, he said: "All probabilities are open."

Christians in Aleppo, speaking on condition of anonymity, told Agence France-Presse gunmen had killed the bishops' driver.

In September, Ibrahim told Reuters hundreds of Christian families had fled Aleppo as rebels and soldiers battled for control of the country's biggest city.

"In its modern history Aleppo has not seen such critical and painful times," he said. "Christians have been attacked and kidnapped in monstrous ways and their relatives have paid big sums for their release."

Archbishop Ibrahim had been supportive of Assad and had urged his followers not to abandon Syria, but he had recently turned critical of the government, the New York Times reports.

Meanwhile, the rebel’s political arm, the National Coalition for Syrian Revolutionary and Opposition Forces, chose a caretaker leader to replace Sheik Moaz al-Khatib until a formal election is held. Sheik Moaz, a Sunni cleric, was temporarily succeeded by George Sabra, a leftist Christian dissident and outspoken critic of Assad.