New York (CNN Business) A FedEx pilot was recently detained by Chinese authorities in Guangzhou, a city in southern mainland China. It's the latest in an escalating conflict between the shipping company and the Chinese government.

The Hong Kong-based pilot, Todd Hohn, was trying to board a commercial flight home after making a delivery to mainland China, when he was arrested after a luggage search, according to a Wall Street Journal report citing a family lawyer for Hohn.

Hohn was carrying "nonmetallic pellets used in low-power replica air guns," leading Chinese authorities to allege he was illegally carrying ammunition, the Journal said.

China's foreign ministry confirmed on Friday that a FedEx pilot was detained at Guangzhou airport on September 12 after 681 air-filled pellets were found in his luggage.

Customs officials at the airport detained the pilot on allegations of smuggling weapons and ammunition and later released him on bail pending trial, ministry spokesman Geng Shuang said in a press briefing. Geng did not name the pilot.

FedEx said the pilot has been released on bail, though the Journal report states he must remain in mainland China until Chinese authorities have completed their investigation. Hohn is a former US Air Force pilot.

"We are working with the appropriate authorities to gain a better understanding of the facts," FedEx said in a statement.

Tensions between FedEx and Chinese authorities have escalated as the larger US-China trade war drags on. The company has also been caught up in the conflict between pro-democracy protesters in Hong Kong and the Chinese government.

The Chinese government began investigating FedEx in June when Chinese tech company Huawei said FedEx diverted two packages to the United States that were meant for Huawei's headquarters in China. The following month, Chinese authorities claimed FedEx was holding back more than 100 packages meant for Huawei. FedEx later sued the US government over export restrictions on Huawei, saying they put FedEx in a vulnerable position.

More recently, Chinese authorities opened another investigation into the company for allegedly shipping a parcel of knives to Hong Kong.

In the wake of the Hong Kong protests, which have become increasingly violent and are now going on 15 weeks , Chinese authorities have ramped up security at travel checkpoints between the city and mainland China.

CNN's Matt Rivers reported last month he and other travelers faced unusually aggressive security, including hours of detainment and questioning, while traveling by train to Hong Kong and back to mainland China. Some other travelers even had their phones searched by authorities.