The US supreme court has handed the case of a transgender teenager who wants to use the boys' toilets at his high school back to a lower court without reaching a decision.

Transgender students have lost the US government protection that allowed them to use school toilets and locker rooms matching their gender identities as Donald Trump's administration stepped into a long-simmering national debate.

A school in Virginia can block a transgender male from using the boys' toilets when term starts next month, the US Supreme Court ruled.