CAIRO, Aug. 16 -- The defence pact signed in Mecca last week is already drawing a fourth member, or at least the prospect of one. Turkish President Recep Tayyip Erdogan said Sunday that Egypt's entry into the nascent Turkey-Saudi Arabia-Pakistan security alliance is "among the options for future expansion," the first public signal that the agreement signed in the holy city may be designed to grow.

Erdogan's statement, made in an interview with Al Jazeera, came just days after he, Saudi Crown Prince Mohammed bin Salman, and Pakistani Prime Minister Shehbaz Sharif formalized a mutual defence commitment that analysts have compared to NATO's Article 5 architecture. Under the Mecca Pact, an armed attack on any one signatory is treated as an a...