Turkish President Tayyip Erdogan said on Saturday that he told his foreign ministry to expel the ambassadors of the United States and nine other Western countries for demanding the release of philanthropist Osman Kavala.

Seven of the ambassadors represent Turkey's Nato allies and the expulsions, if carried out, would open the deepest rift with the West in Erdogan's 19 years in power.

Kavala, a contributor to numerous civil society groups, has been in prison for four years charged with...