China on Monday called on the US’ FedEx to explain why a parcel from Huawei to the US went undelivered, in the second spat between the companies in less than a month.

The ongoing tussle between the two firms comes as Beijing and Washington face off in a trade war in which both sides exchanging steep tariffs on hundreds of billions in exports.

IT publication PC Mag said on Friday a FedEx package with a Huawei phone inside that it had sent to the US was returned to the UK.

An accompanying note explained a US government “issue” with China prevented the delivery.

FedEx apologised for the incident.

“The package in question was mistakenly returned to the shipper and we apologise for this operational error,” a company spokesperson said in a statement.

“As a global company that moves 15 million shipments each day, we are committed to compliance with all rules and regulations and minimising impact to our customers as we adjust our operations to comply with a dynamic US regulatory environment.”

The US logistics group is already under investigation in China for failing to deliver some of Huawei’s parcels.

“This is not the first time FedEx has made a Huawei-related mistake,” said Geng Shuang, spokesman for China’s Ministry of Foreign Affairs.

“FedEx, as a large multinational company, should give a reasonable explanation to the outside world and be responsible for its own actions.”

On Friday, a journalist at PC Mag sent out a tweet of a photo of a package along with a note reading: “Parcel returned by FedEx, due US government issue with Huawei and China government”.