A judge in Pakistan asked the police to file formal charges against an FBI agent arrested after allegedly carrying ammunition and three knives onto an airplane.

FBI agent Joel Cox was set free on bail on 1 million rupees ($9,800). Police investigator Khalid Mahmood said Mr. Cox appeared on Saturday before a judge in Karachi, the capital of southern Sindh province.

Mr. Mahmood said police told the judge they need more time to file formal charges. Mr. Cox is expected to be back in court on May 19.

Mr. Cox arrived in Karachi on May 1 and was detained on Monday after officials found him with the ammunition, knives and electronic devices as he was preparing to board a flight to Islamabad.

The arrest is a new strain on relations between Pakistan and the U.S.