France has modified its official advice to nationals travelling to the United States, warning they must now state their gender assigned at birth in visa or ESTA applications.

It stopped short of warning, as Denmark did recently, that transgender people could be barred from entering the US as a result of a decree signed by President Trump on 20 January.

But potential visitors are "strongly recommended" to check the website of the US embassy in Paris "for any changes or new measures adopted", the French foreign ministry said in an update to its travel advice published overnight on Monday to Tuesday.

The Trump decree states that the US government only recognizes the gender assigned to a person at birth, ruling out the possibility of marking "X" to indicate a non-binary status, or declaring a different gender.

"In particular, for new visa or ESTA applications, it is important to note that a section has been added that requires... applicants to state their 'gender assigned at birth'," the foreign ministry in Paris said.

ESTA, which stands for "Electronic System for Travel Authorization", is an automated system to determine the eligibility of visitors to the US under its visa waiver program.

An ESTA, valid for visits up to 90 days, does not guarantee admission to US territory, however. 

The final decision is up to border officials on a visitor's arrival.

Nationals of dozens of countries are eligible for an ESTA, including France.

The ministry said it had no knowledge of any French national being denied entry to the US because of a gender-related question.