> "[...] worked to establish international consensus on the effects of the accident via a series of reports that collated 20 years of research to make official previous UN, IAEA, and World Health Organization (WHO) estimates of a total of 4,000 deaths due to disaster-related illnesses."
In fact, the sentence you quoted states:
> "[...] there is considerable debate concerning the accurate number of deaths due to the disaster's long-term health effects, with estimates ranging from 4,000 (per the 2005 and 2006 conclusions of a joint consortium of the United Nations and the governments of Ukraine, Belarus, and Russia), to no fewer than 93,000 (per the conflicting conclusions of various scientific, health, environmental, and survivors' organizations)."
So it's not just Russia.