US delivery firm FedEx allegedly sent controlled knives to Hong Kong, according to the Xinhua News Agency on Tuesday. 

Chinese mainland branch of FedEx allegedly accepted mail parcels that contain controlled knives destined for Hong Kong, the Xinhua report said, noting that the items are being withheld by the Chinese authorities and a probe is underway.

There are currently no more details on the matter.

The US delivery company is involved in the delivery of a gun, which is strictly forbidden in China, in August. 

The company also "misrouted" mail parcels belonged to Chinese telecommunication company Huawei amid a US government crackdown on the Chinese technology giant and caused Chinese authorities to open an investigation into it.

The company's action has led to calls to put it on China's unreliable entity list, which is in the process of being rolled out. Under the mechanism, China can blacklist foreign companies on national security grounds. 

The parcel's destination is very sensitive at the moment. 

In Hong Kong, anti-government protesters have escalated their violence recently, as they, most of the time, intentionally aimed to attack and injure police officers who confronted them amid riots. According to the offensive weapons that the police have seized from radical protesters, items such as daggers and hammers as well as knives are commonly seen.  When the police arrived to disperse the crowds at Yeung Uk and Tsing Tsuen roads on August 25, which were illegally occupied by violent protesters, the individuals still threw gasoline bombs at the police and attempted to attack the police with knives.

Also, an off-duty officer at Kwai Chung police station was injured in a knife attack on Friday, after he was attacked by three knife-wielding men in black, according to local media reports.