US President Donald Trump's controversial ban on transgender Americans in the military comes into force on Friday following a protracted legal battle. Trump's administration has insisted that there is "too great a risk to military effectiveness and lethality" to allow transgender people to serve – reversing a policy enacted under his predecessor Barack Obama.

The Pentagon says the restrictions are not a blanket ban. Trump first announced the policy on Twitter in July 2017. It has been repeatedly challenged in court. The US Supreme Court ruled in January the policy may take effect pending the outcome of ongoing litigation.