US claims to a swath of mineral-rich seabed are being challenged by China and Russia because Washington has failed to ratify a treaty that governs access to resources in international waters.

Chinese and Russian diplomats said last week that a US claim to an extended area of seabed was unacceptable given its position on the 1982 United Nations Convention on the Law of the Sea (Unclos), according to three people who attended a meeting in Kingston, Jamaica of the International Seabed Authority, which was established under the treaty.

Hundreds of former US government officials and military officers recently wrote to Senate leaders urging the body to ratify Unclos. This would ensure that the US could harvest critical minerals from the ocean floor once the ISA has agreed regulations for deep-sea exploration, which may come next year.