A group of Americans who disappeared in Baghdad over the weekend were kidnapped from their interpreter's apartment, according to multiple Iraqi sources.
The apartment is well-known in southern Baghdad as a brothel and is subject to frequent raids by Shiite militias, including the Iran-backed Asa’ib ah al-Haqq, a police official and a building resident told The Washington Post.
An Iraqi intelligence official told the Associated Press that the Americans were invited into the apartment in the neighborhood of Dora. After they were abducted, they were taken to Sadr City, at which point the official said, "all communications and contact stopped."
A spokesman for Baghdad's Joint Operations Command told The Washington Post that the three citizens were Iraqis who had acquired U.S. citizenship. A Baghdad police official said they worked as contractors at Baghdad International Airport, but did not say which country employed them.
The U.S. Embassy in Baghdad confirmed Sunday that "several" Americans had vanished, while the State Department said it was working with the Iraqi government to locate them.
The rest of the article speculates about ISIS' involvement, but I think it's clear that if they were taken to Sadr City, they must have been abducted by Shi'a militias, possibly on the orders of Iran.