TEHRAN, Iran (AP) – Britain’s Foreign Office is advising against all travel to Iran by British-Iranian dual nationals.

The government said Friday the upgraded travel warning is in response to Iran’s “continued arbitrary detention and mistreatment” of dual nationals and of Iranian citizens working for institutions linked to Britain.

It follows the arrest of an Iranian woman who had been working for the British Council in Iran.

Foreign Secretary Jeremy Hunt said dual nationals face an “intolerable risk” of abuse if they travel to Iran.

He cited the case of Nazanin Zaghari-Ratcliffe, a dual citizen detained in Iran since 2016.

The Foreign Office also warns that Iran does not recognize dual nationality, limiting the British government’s ability to help dual nationals detained in Iran.