But who the group is and what its relationship might be to other Salafi groups calling themselves “tawhid” was unknown.

Analysts in the United States who specialize in researching the rebels said they believe the “tawhid” now operating in Aleppo represent a previously unappreciated rebel organization that may influence the activities of as many as 36 individual components known to have fought elsewhere in Syria. But those analysts, too, say they are uncertain what ties, if any, the group might have to the general “tawhid” movement.

Meanwhile, for the first time since the uprising against Assad began in March 2011, the presence of dozens of foreign Islamist fighters was confirmed Friday by two journalists who’d been held by a group of them near the border with Turkey for a week.

Jeroen Oerlemans, a Dutch freelance photographer, told the NRC Handelsblatt newspaper that he and British photographer John Cantlie were held for a week by the group, which they accidentally encountered after they’d crossed into Syria surreptitiously from Turkey.

Oerlemans said the group of about 20 included a Pakistani who spoke English and “a number of Africans” and “many Central Asians.” He described them as “foreign jihadists.”

"One of the black jihadists freaked out and shouted: ‘These are journalists and now they will see we are preparing an international jihad in this place,’" Oerlemans told the paper.

In the days they were held, Oerlemans said, they met other foreign combatants. “We met many combatants who spoke good English, some with Birmingham accents,” he said, referring to the British city that has a large immigrant population. “They see Syria as the last battlefield. But first Assad must be toppled. So they fight against the same opponent as the Free Syrian Army, only with a different purpose. As soon as Assad has fallen, these fighters want to introduce Islamic law, Sharia, in Syria.”

“I immediately felt sorry for the fighters of the Free Syrian Army,” Oerlemans said. “You get rid of Assad, and the first thing you have to deal with is these guys.”

Oerlemans said the photographers and their guide, who spoke no English, attempted to escape on the second day they were held. But they were quickly detected as they were running toward Turkey and shot, Oerlemans in the hip and Cantlie in the arm. What became of their guide in unknown.

The two photographers were held until Thursday, when four Free Syrian Army rebels showed up in camp and took them away. “Just like we never expected to be kidnapped by jihadists, being freed this way was even more surprising,” Oerlemans said. “Three hours later we were in Turkey.”

Concern about the involvement of foreign fighters in the anti-Assad rebellion is a question that has curtailed Western enthusiasm for providing weapons to the insurgents. Free Syrian Army rebels have denied any links to the jihadists and have openly criticized Western intelligence analysts who’ve blamed some of the most spectacular anti-Assad bombings on al Qaida or al Qaida-affiliated organizations.

But the same group that apparently held Oerlemans and Cantlie also claimed the capture 10 days ago of the Bab al Hawa border crossing between Syria and Turkey. The group, which calls itself Shura Al Taliban, posted a video of the capture of the crossing on YouTube before withdrawing.

Syrian rebels have said repeatedly that they would not allow foreign fighters with an Islamist agenda to get in the way of their goal of toppling Assad, but they have acknowledged the presence of Iraqi, Libyan and Palestinian fighters in their ranks previously, in small numbers.