The US Consumer Products Safety Commission on Tuesday ruled that Amazon is responsible for hazardous items sold on its website by third-party sellers and that it must create a plan to notify consumers about unsafe products and to provide refunds or replacements.

The CPSC order cited items that include defective carbon monoxide detectors, children's sleepwear that violates flammability standards and hair dryers that lack electrocution protections. Altogether, the agency said, more than 400,000 products are affected by the order.

The third-party sellers participate in the Fulfilled by Amazon program, according to the CPSC.

In addition to the items themselves posing a "substantial product hazard," the agency said, "Amazon failed to notify the public about these hazardous products and did not take adequate steps to encourage its customers to return or destroy them, thereby leaving consumers at substantial risk of injury." 

Amazon didn't immediately respond to a request for comment. 

Last year, Amazon debuted a recall and safety alerts page on its site.

In recent years, agencies including the CPSC, the US Food and Drug Administration, the National Highway Traffic Safety Administration and the US Department of Agriculture have stepped up recalls of products. Electric vehicles, Tide detergent pods and Pack and Play infant beds (which were sold exclusively on Amazon) are some of the items recalled this year.

Three years ago, the CPSC sued Amazon, alleging its unwillingness to remove unsafe third-party products sold through its site.

Prior to Tuesday's decision, the CPSC says, Amazon did not dispute whether the items were unsafe, arguing instead that it was not acting as a distributor of hazardous products as defined by the Consumer Product Safety Act and therefore was not responsible for taking actions to protect the public.

The commission and a judge on the case determined otherwise. The CPSC ruled that Amazon was a distributor of the products in question and said that the e-commerce giant's actions were "inadequate to protect the public."

Amazon must submit a plan to the CPSC describing how it intends to notify consumers and the public about the hazardous products and to provide incentives for their return or destruction. The agency will review those plans and issue a subsequent order. It did not provide a timetable.