VICTORIA FALLS, Zimbabwe — Zimbabwe’s diamond conference was rocked by controversy Tuesday over the Kimberley Process, the world diamond trade regulatory body, whose chairwoman was publicly asked to resign because she is American.

Gillian Milovanovic, the American chairwoman of the Kimberley Process, came under a barrage of criticism from African delegates at the Zimbabwe Diamond Conference for allegedly not doing enough to persuade the US government to lift trade restrictions on Zimbabwe’s state-owned diamond mining companies.