“We take seriously our responsibility to assist US citizens abroad and are monitoring the situation,” the spokesman said in a statement.

Under Chinese law, suspects released on bail cannot leave the city without permission. Authorities can also seize the person’s passport and limit their activities and communications.

The Wall Street Journal, which first reported on the case, identified the pilot as former US Air Force colonel Todd Hohn, a resident of Hong Kong.

According to the report, Hohn was detained while waiting in an executive lounge to board a flight with Cathay Dragon, a subsidiary of Hong Kong’s embattled flagship airline Cathay Pacific Airways. Hohn was told that he could not leave mainland China until the investigation concluded, the report said.

FedEx denies wrongdoing after China accuses it of shipping ‘controlled knives’ to Hong Kong

In a statement, FedEx confirmed that one of its pilots was detained and later released on bail after “an item was found in his luggage before a commercial flight”.

“We are working with the appropriate authorities to gain a better understanding of the facts,” the company said.

The Tennessee-headquartered multinational, which began operations in China in 1984 and started flying its own aircraft into the country a decade later, has found itself in Beijing’s cross hairs recently as the US-China trade war has escalated. The two sides resumed face-to-face talks in Washington on Thursday for the first time in nearly two months.

In May, FedEx was accused of knowingly shipping packages meant for technology firm Huawei in China to the United States, only days after Huawei was put on a US government blacklist banning American firms from selling products to the telecommunications giant.

FedEx apologised on its Chinese social media account for the “mis-transportation” of the packages, saying they were diverted in error. But Ma Junsheng, head of China’s State Post Bureau, said in early June that the government had launched a formal investigation.

China police investigating FedEx package containing handgun sent from US to Chinese sporting goods firm

In August, FedEx was accused of allowing a gun to be shipped from the US to a Chinese sportswear company in Fujian province. FedEx said it discovered the gun and turned it over to local authorities.

Then earlier this month, state news agency Xinhua said regulators were investigating FedEx for trying to ship controlled knives to Hong Kong. The firm denied the accusation, saying the shipment in question “was handled correctly via standard security protocol”.

China is expected to soon launch its first “unreliable entity list” of foreign firms sanctioned by Beijing for engaging in illegal activities or in non-commercial activities that harm Chinese companies. Some Chinese state media outlets have said that FedEx could be put on the list.

It is plausible that China has issued instructions to local authorities to “harass” FedEx, said Jorge Guajardo, a former Mexican ambassador to China.

“But I do not see this episode with this pilot as part of a broader campaign to sort of pressure the United States,” said Guajardo, who added that China would have much to lose should it enter a tit-for-tat strategy of arrests with the US in the same way it has targeted Canadian nationals after the detention of Huawei executive Meng Wanzhou in Vancouver on December 1.

“If they go for a full blown-out campaign of arresting each other’s citizens, you have a lot of children of high or very powerful Chinese government officials in the United States who could be subjected to this,” said the former diplomat, now a senior director at McLarty Associates in Washington.

Noting that it was uncommon for a foreign national to be released on bail in China, Guajardo said it was also possible that central authorities had intervened in Hohn’s case to avoid angering the US, with whom high-level trade negotiations are anticipated for mid-October.

The State Department spokesman declined to answer questions on Friday about whether the US government was concerned that Hohn had been arbitrarily targeted because of his nationality.

The department’s current travel advisory for China warns US nationals to “exercise increased caution” while visiting the country because of “arbitrary enforcement of local laws.”