KARACHI, Pakistan — A judge in southern Pakistan asked police Saturday to file formal charges against an FBI agent arrested there after allegedly carrying ammunition and three knives onto an airplane, an investigator said.

FBI agent Joel Cox, free on 1 million rupees ($9,800) bail, appeared along with his lawyer before Judge Mohammed Ali Memon in Karachi, the capital of southern Sindh province, Khalid Mahmood told The Associated Press.

Mahmood said police told the judge during a brief hearing they needed more time to file formal charges,.

Memon told police to submit the charges against Cox on May 19. The FBI agent is expected to be back to the court that day.

Cox arrived in Karachi on May 1 and was detained 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. The U.S. needs Islamabad to help contain militancy on the border with Afghanistan, but the two countries have been uneasy allies since the Sept. 11, 2001, terror attacks.

Their ties have been tested by incidents like CIA contractor Raymond Davis shooting and killing two Pakistani men in Lahore in January 2011. The U.S. unilaterally killed Osama bin Laden in the Pakistani city of Abbottabad in May 2011 and American forces accidentally killed 24 Pakistani troops along the Afghan border the same year. U.S. drones strikes in the country also have angered Pakistanis.

Mahmood said the FBI agent's passport was with police, although no court has issued an order to stop him from traveling abroad. Pakistani officials have said they found that Cox had no criminal intention in carrying the bullets during the flight.