The FBI agent, who was previously identified in the press as Joel Cox but whom American officials have declined to identify, was released on $10,000 bail and handed over to the U.S. Consulate in Karachi.
U.S. Department of State spokesperson Jen Psaki commented Wednesday on the incident:
"We are coordinating with Pakistani authorities to resolve this matter. This individual detained is an employee of the FBI who was on a temporary duty assignment to provide routine assistance to the legal attache at the U.S. mission. But we are coordinating closely to resolve this manner with authorities, and we are hopeful in that regard."
Cox is facing anti-terrorism charges. He appeared in court Tuesday and is scheduled in court again on Saturday.
Under Pakistani law, unauthorized weapons and ammunition are restricted on commercial flights. With Pakistani authorization, FBI employees and other U.S. agency personnel can carry weapons in Pakistan.
U.S. officials said that Cox had accidentally left the ammunition in his luggage.