More than 50 retired generals and admirals in the US have spoken out against President Trump's proposed ban on transgender troops.

The US president last week took to Twitter to claim that "the United States Government will not accept or allow transgender individuals to serve in any capacity in the US military".

He suggested that US forces "cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail".

If implemented, the ban would serve as a reversal of Barack Obama's policies, and it was unclear how it would impact the thousands of transgender personnel believed to be currently serving.

However, military officials in the US indicated that there would be no change to existing policy unless they received formal directions from the president. 

In an open letter published by the Palm Center research institute, 56 retired senior officers have criticised the proposed ban.

They write: "This proposed ban, if implemented, would cause significant disruptions, deprive the military of mission-critical talent, and compromise the integrity of transgender troops who would be forced to live a lie, as well as non-transgender peers who would be forced to choose between reporting their comrades or disobeying policy.

"President Trump seeks to ban transgender service members because of the financial cost and disruption associated with transgender military service. We respectfully disagree, and consider these claims to be without merit."

They add that there is "no reason" to single out "brave men and women and deny them the medical care that they require".

According to the The Guardian, a Rand Corporation study estimated that gender-transition-related medical expenses would cost the US military between $2.4 million and $8.4 million annually - a tiny fraction of the Pentagon's $6.27bn annual healthcare costs for all active-duty personnel.