LONDON — Condé Nast International said Thursday that Vogue editors worldwide were clamping down further on the use of underage models, following two separate incidents at Vogue, in China and in Japan.


A Condé Nast statement said that all modeling agencies will now be asked to provide documentary proof of the age of models who are not well known, otherwise they will not appear in the magazine.


The statement follows the discovery that a 15-year-old model appeared in the August edition of Vogue China in an article on up-and-coming models. The editor, Angelica Cheung, has apologized.


Separately, Japanese Vogue said it unwittingly used an underage model in an advertising promotion photo shoot set for the December issue. The promotion has since been pulled.


In June, 19 Vogue editors worldwide announced they would adhere to the Vogue Health Initiative, which aims to promote a healthier approach to body image within the fashion industry and to ensure that underage models are not employed.


Jonathan Newhouse, chairman and chief executive of Condé Nast International, said in the statement: “The Health Initiative banning underage models is very serious, and we will reinforce it. I apologize for the error that took place in China. We will do everything possible to prevent future errors.”


Condé Nast pointed out that occasionally Vogue will publish an article or supplement devoted to children’s apparel, and that the ban on young models does not apply to articles about children dressed in age-appropriate clothing.