The official, who spoke on condition of anonymity because he was not authorised to discuss the situation, said the man is being held by the Haqqani network, a family-run militant group that operates along the Afghanistan-Pakistan border.
The official would not discuss the man's identity or the circumstances of his capture. The incident was first reported Wednesday by the Daily Beast web site.
Operation under way to rescue abducted officials
The FBI, the White House and the man's wife have urged public officials and media organisations not to discuss the matter publicly, the official said.
The White House declined to comment, and the State Department declined to confirm the man's capture.
The department is "aware of reports that an American is being held," spokesman Mark Toner said, and "we reiterate our calls for US citizens being held hostage around the world to be released."
On Monday, Rep Duncan Hunter (R-CA), who has been critical of US hostage recovery efforts, wrote a letter to President Obama urging that he appoint a federal hostage coordinator.
In the letter, he noted that "there are still Americans in captivity in the Afghanistan-Pakistan region."
Abducted Pakistani workers freed in Afghanistan
The only other known American captive there is Caitlin Coleman, who was kidnapped along with her husband, Canadian Joshua Boyle, while traveling in Afghanistan in 2012.
American officials call the Haqqani network a terrorist organisation and have targeted its leaders with drone strikes. But the group also operates like a criminal network. Unlike the Islamic State, it is not in the habit of executing Western hostages, preferring to ransom them for cash.
This article originally appeared on The New York Times, a partner of The Express Tribune.
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