The World Health Organization said it has asked China to provide more information on an outbreak of pneumonia among children in northern parts of the country, an unusual public disclosure that revives questions about Beijing’s transparency on the spread of infectious diseases.

In a statement issued Wednesday, the WHO cited reports about “clusters of undiagnosed pneumonia in children in northern China,” which prompted the United Nations agency to ask Beijing for “additional epidemiologic and clinical information, as well as laboratory results” related to the infections.