The U.S. military will effectively bar most transgender people and force people to serve under their birth gender, according to a memo from the Department of Defence.

The new rules will go into effect on April 12.

While they do not fully conform with President Donald Trump’s attempt to ban transgender people from serving in the military, the new policy takes a large step in that direction.

People currently undergoing treatment for gender dysphoria may continue to serve.

However, from April, those in the process of ‘transition’ will not be allowed to join the military.

“The Trump administration is once again cruelly and unfairly targeting transgender people who have been serving this country for years,’’ said GLAAD, a legal advocacy group.

Adam Smith, the chairman of the House of Representatives Armed Services Committee, came out against the new rules and called for the Department of Defence to refrain from implementing them.

“Anyone who is qualified and willing should be allowed to serve their country openly.

“Make no mistake, this is a discriminatory ban on transgender people, not a ban on a medical condition and we will continue to fight against this bigoted policy,’’ said Mr Smith.

Transgender people were allowed to openly serve in the army from 2016 in a policy implemented by a former president, Barack Obama.