KARACHI, Pakistan — Police in Pakistan questioned an American on Wednesday who a U.S. government source said is an FBI agent on an anti-corruption task force, officials said.

The arrest marked the latest incident to trouble relations between Pakistan and the U.S., two uneasy allies since the Sept. 11, 2001, terror attacks.

Pakistani police officer Rao Anwaar declined to say whether the detained American was the FBI agent. He said investigators hadn’t received any written evidence proving the man worked for the U.S. Embassy in Pakistan.

The American arrived in Karachi on May 1 and was detained Monday when he was about to board a flight for Islamabad, Anwaar said. He said officials found the man carrying ammunition and three knives, as well as electronic devices that were being examined.

A law enforcement official in the U.S. identified the man as an FBI agent and said he was in Pakistan as part of a multiagency, anti-corruption program.

The off icial said the agent appears to have made a mistake and that there’s no indication he was trying to carry bullets aboard the plane. The official said authorities are hopeful the situation will be resolved soon with the agent’s release.

The official, who did not provide the agent’s name or age, spoke on condition of anonymity because of the diplomatic sensitivities of the case.

A Section on 05/08/2014