US television network NBC News has altered its account of the 2012 kidnapping of its top foreign correspondent, saying the masked men who snatched him and his team in Syria were Sunni militants, not Assad forces.

The story was the latest setback for NBC, which is reeling from the suspension of star news anchor Brian Williams after he admitted embellishing an Iraq war story and amid accusations he embellished other stories.

In a statement posted late Wednesday on NBC's website, chief foreign correspondent Richard Engel said a review of the kidnapping found that "the group that kidnapped us was Sunni, not Shia."

But he blamed the error on an "elaborate ruse" by the kidnappers to convince Engel and his five colleagues that they had been seized by a Shiite militia loyal to Syrian President Bashar al-Assad known as the shabiha.

The review came after The New York Times contacted NBC about the story, and Engel said he reached the new conclusion after contacting "multiple" US law enforcement and intelligence sources with direct knowledge of the case.

Engel and his team were kidnapped for five days in December 2012, and immediately after their release appeared on the network's "Today" morning show.

The Times said Engel's team was likely taken by a Sunni gang linked to the Free Syrian Army alliance of anti-Assad rebels.

The group, known as the North Idlib Falcons Brigade, was led by Azzo Qassab and Shukri Ajouj at the time. And, the newspaper said, the kidnapping ended when a separate rebel group, Ahrar al-Sham, freed Engel and his team.

NBC executives were told of Qassab and Ajouj's possible role in the kidnapping, former NBC employees and others involved in the search told the Times.

But Engel nonetheless blamed Shiite captors on air.

NBC is separately under growing pressure to fire the 55-year-old Williams, who reportedly earns about $10 million a year and has scooped up more than two dozen industry awards during his glittering journalism career.