White House: Robert Levinson not a government employee
The White House has said the ex-FBI agent believed to have been held in Iran for the last seven years was not working for the US government at the time of his disappearance.
White House spokesman Jay Carney spoke the day after the Associated Press news agency reported Mr Levinson was on an unauthorised mission for the CIA.
He has been missing since March 2007.
Mr Carney declined to comment on what Mr Levinson was doing in Iran at the time he disappeared.
The Associated Press report, which Mr Carney labelled "highly irresponsible", says Mr Levinson had done contract work for the CIA in his capacity as a former FBI expert in Russian organised crime.
But at the time Mr Levinson disappeared, his CIA contract was out of money, though the CIA analysts with whom he was working were trying to authorise more, the AP reported.
'A top priority'
Mr Carney said there remained an ongoing investigation into Mr Levinson's disappearance, and dismissed accusations by Mr Levinson's family that the US government had not done all it could to locate him.
"Since Bob disappeared the US government has vigorously pursued and continues to pursue all investigative leads," Mr Carney said. "We continue to be focused on everything we can to bring Bob home safely to his family. This remains a top priority of the US government."
The Associated Press report alleges Mr Levinson was in Iran on an unapproved intelligence-gathering mission that, when revealed, caused serious tumult within the CIA.
The US agency reportedly paid Mr Levinson's family $2.5m (£1.5m) to avoid a public lawsuit, and also disciplined 10 veteran analysts.
The team of analysts is said to have paid Mr Levinson to gather intelligence prior to his disappearance.
Three of the CIA analysts who hired him - who reportedly had no authority to run spy operations - were allegedly later forced out of the agency.
The media outlet says it was asked by the US government three times since 2010 to hold the story about Mr Levinson's CIA ties.
The news agency said it decided to run the report after all efforts to locate and free Mr Levinson seemed to have failed.
On Friday, Mr Carney said the US government "strongly urged the outlet not to publish out of concerns for Mr Levinson's safety".
Neither the identities of the former FBI agent's captors nor his whereabouts have been confirmed, but US officials asked for Iran's assistance in finding him just days after Iran and Western powers signed an interim agreement aimed at curbing Iran's nuclear programme in late November.
Former Secretary of State Hillary Clinton has said she believed Mr Levinson was being held in south-west Asia.
Mr Levinson, 64 when he went missing, was initially said to have been investigating cigarette counterfeiting as a private detective when he disappeared.
His family received images of Mr Levinson in April 2011, showing him wearing a long grey beard and an orange jumpsuit, and looking gaunt.
The family were also sent a video in November 2010, which they released in December 2011 to try to aid the investigation.
In the 54-second clip, Mr Levinson pleads: "Help me get home."
Iran has said it does not know where Mr Levinson is and that there is no evidence he is in the country.
Investigators traced the phone used to send the photographs to Afghanistan, but the phone's owner was not involved. The video was sent from a Pakistan internet cafe.