U.S. government sources say three U.S. citizens who disappeared in Baghdad last week were abducted and are being held by an Iranian-backed Shi'ite militia, Reuters has reported.
The information was based on reports from two Iraqi intelligence and two U.S. government sources.
Iraqi officials said unknown gunmen seized the three men on January 15 from a private residence in Baghdad's Dora district.
They are the first U.S. citizens to be kidnapped in Iraq since the withdrawal of U.S. combat troops in 2011.
U.S. State Department spokesman John Kirby said on January 19 that Washington is "working very closely with Iraqi authorities to try to get more information" about the three.
"Without getting into details, I can tell you that the picture is becoming a little bit more clear in terms of what might have happened," Kirby said.
U.S. sources told Reuters that Washington had no reason to believe Tehran was involved in the kidnapping and does not believe the three are being held in Iran.
The men were reportedly employed by a company working under a contract with the U.S. Army.
U.S.-Iranian relations have improved in recent months with the lifting of economic sanctions against Iran after an international deal that curbs Tehran's nuclear program as well as a prisoner swap between the two countries last weekend.
But Iranian officials were angered when Washington subsequently announced new sanctions for a string of ballistic-missile tests by Iran.