The Chinese postal service has offered to help investigate the source of mysterious packages of seeds that have been appearing in people's postboxes in the United States.
Residents across the US have reported receiving unsolicited packages from China, often marked as containing toys or jewellery.
The types of seeds have yet to be identified and agriculture officials have warned residents not to plant them in case they prove to be harmful or invasive species.
On Tuesday, Chinese foreign ministry spokesman Wang Wenbin told a regular press briefing: "China Post has asked the United States Postal Service to return this faked mail to China so China can investigate."
Wang said information labels on the packages appeared to be forged, according to checks by China's postal service, adding that there were errors in the information attached to the packages.
Wang also said the Chinese postal service strictly adhered to the Universal Postal Union's rules about handling seeds.
The mystery packages appeared at a time of growing tension between the two countries, including the recent tit-for-tat consulate closures.
Agriculture officials in at least 27 states have warned people who receive the seeds not to plant them and contact the authorities.
The Virginia department of agriculture was one of the departments to warn that they might contain invasive species which "wreak havoc on the environment, displace or destroy native plants and insects and severely damage crops".
"Right now, we are uncertain what types of seeds are in the package," Mike Strain, the commissioner of the Louisiana Department of Agriculture and Forestry, said in a statement.
"We need to identify the seeds to ensure they do not pose a risk to Louisiana's agricultural industry or the environment."
However, the police department in Whitehouse, Ohio, suggested on its Facebook page that the seeds may be part of a "brushing" scam.
Under this guerilla marketing practice, a business sends its products to unsuspecting recipients whose names and addresses have been acquired from third-party sellers. It then writes fake reviews posing as the "customer".
- South China Morning Post