"The US embassy has raised the issue and hope such incident will not be repeated in future," the Daily Times quoted US officials as saying.
The Committee to Protect Journalists has demanded a probe into the matter.
"Pakistani authorities must investigate this incident immediately and assure that journalists are allowed to work freely," said CPJ Executive Director Joel Simon.
"We are alarmed by the use of government security services to harass journalists reporting in Pakistan on issues of global significance," he added.
Earlier, Carlotta Gall, a New York Times reporter covering Pakistan and Afghanistan, told the committee that the special branch police "harassed her and photographer Akhtar Soomro in Quetta on December 19."