Washington State Department of Agriculture / Reuters
The unidentified seeds appear to have been shipped to US addresses from China
Amazon says it banned the sale of seeds overseas in the US after thousands of Americans received unsolicited packages of seeds in the mail, most of them from China.
The online retail giant told the BBC that the sale of seeds would only be allowed by sellers based in the United States.
US officials said gardeners should not plant seeds of unknown origins.
The packages are believed to be part of a global "brushing" scam in order to get positive reviews for online sales sites.
Amazon's new guidelines, in effect since September 3rd, also prohibit the sale of seeds within America by non-US citizens. Added that sellers may get banned if they don't follow the new guidelines.
However, the retailer has not confirmed whether its ban extends to other countries.
The Wall Street Journal first reported on the policy change.
At least 14 species of plants were identified among the mystery packages, including mint, lavender and roses.
Amazon says it will only allow domestic sales of seeds in the US
Unsolicited seed packages are also reported in other countries, including the UK. Last month, Scottish authorities advised people not to handle the seeds for fear they could damage local ecosystems.
In an August 11 update, the U.S. Department of Agriculture (USDA) said that experts who analyzed the seeds found few problems with them and that China was helping with the investigation.
However, the USDA has warned people against planting seeds, saying they could be non-native species or carry pests and diseases.
In so-called "brush" scams, sellers send items of little value such as seeds or rings. Each fake "sale" then generates an online review that appears to strengthen the seller's legitimacy.