FedEx says one of its pilots was detained in China after an item was found in his luggage before he boarded a commercial flight.

The company said today the pilot was later released, and it is working with Chinese authorities to understand what happened at the airport in Guangzhou, in southern China.

The Wall Street Journal reported that former U.S. Air Force pilot Todd A. Hohn was detained on Sept. 12 after pellets used in replica air guns were found in his checked bag. The paper cited people familiar with the incident.

The newspaper said Chinese authorities allege that Hohn was illegally carrying ammunition, and they have started a criminal investigation.

“We are working with the appropriate authorities to gain a better understanding of the facts,” a FedEx spokeswoman said in a statement sent to The Associated Press.

FedEx said the pilot was later released, although the company spokeswoman said she did not know where he is now. The Journal reported that Hohn was moved to a hotel and told that he can’t leave mainland China until the investigation is over.

FedEx declined to comment further. It would not say whether the incident has affected its schedule in Asia.

The Air Line Pilots Association, which represents FedEx pilots, has told its members not to comment on social media because of the sensitive nature of an incident in China.

A Federal Aviation Administration database of pilots lists a Todd A. Hohn in Niceville, Florida. He is licensed to fly several different planes including Boeing 757 and 767 jets used by FedEx.

FedEx Corp. has been caught up in rising trade tension between the United States and China.

This week, FedEx CEO Fred Smith blamed slower worldwide economic growth on trade uncertainty. Shares of FedEx fell 12.9% Wednesday — their worst day since 2008 — after the Memphis, Tennessee-based company reported disappointing quarterly profit and cut its estimate of full-year earnings.

Earlier this year, Chinese technology giant Huawei complained about deliveries that FedEx misrouted. Shortly after that, in June, FedEx sued the Commerce Department to stop enforcement of export rules that restrict shipments to Huawei and other entities. Huawei is on a list of companies barred from receiving U.S. technology without a special license from the Commerce Department.