Beginning next month, citizens of the United States will be able to select an “X” for a third gender when applying for a new passport.

This marks another milestone in "serving all US citizens better, regardless of their gender identity," US Secretary of State Antony Blinken said on Thursday.

"Starting April 11, US citizens can select an X as a gender identifier when applying for a US passport." The department is the first US federal agency "to offer the X as a gender identifier in an identification document".

Instead of an "M" for "male" (male) or "F" for "female" (female), people who do not identify themselves with either of these two genders can enter an "X".

The Ministry of Foreign Affairs announced the new regulation in the summer of last year.

In October, the authority issued the very first passport with the entry "X".

Gender identity takes many forms: Not all people classify themselves as male or female.