"This was a group known as the Shabiha. This is a government militia. These are people who are loyal to President Bashar Assad," Engel said on air Tuesday morning.
An NBC news team, including chief foreign correspondent Richard Engel, was freed in Syria Monday after an Islamist rebel group killed two of their kidnappers at a checkpoint, the network reported on its website Tuesday.
The team, which later spoke live on the network, were held captive by an unidentified group for five days.
Engel, 39, and two other members of the news team, disappeared shortly after crossing into northwestern Syria from Turkey on Thursday. The network had not been able to contact them until they were freed.
"It was a very traumatic experience," Engel said on NBC's "Today" program.
Engel, speaking from Antakya, Turkey, said they were not physically beaten but there was psychological torture, including threats of being killed and mock shootings.
The network said the team was bound and blindfolded but not harmed. There was no claim of responsibility and no request for ransom, NBC said.
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"Early Monday evening local time, the prisoners were being moved to a new location in a vehicle when their captors ran into a checkpoint manned by members of the Ahrar al-Sham brigade, a Syrian rebel group," the network said.
"There was a confrontation and a firefight ensued. Two of the captors were killed, while an unknown number of others escaped," it said, adding that the news crew left Syria on Tuesday morning.
Engel said he had "a very good idea" who his captors were.
"This was a group known as the Shabiha. This is a government militia. These are people who are loyal to President Bashar Assad," he said on NBC, adding that the kidnappers spoke openly about their loyalty to the government and their faith.
He said the captors were planning to exchange him and his team for four Iranian agents and two Shabiha members.
Ahrar al-Sham, an extremist Salafist group that includes a large contingent of foreign fighters, has been at the forefront of rebel offensives in the country's north.
Members of the group have told Reuters the unit wants to establish an Islamic caliphate in Syria, not a pluralistic democracy, when Assad is overthrown. But they have not shown hostility to Western journalists covering the conflict.
Engel is an American correspondent who has reported on the popular uprisings that swept the Arab world since 2011.
At least 40,000 people have been killed in Syria's uprising, which started in March 2011 with street protests that were met with gunfire by Assad's security forces, and which spiraled into the most enduring and destructive of the Arab revolts.
Reporting by Oliver Holmes in Beruit and Susan Heavey in Washington.
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