The National Anti-Corruption Bureau of Ukraine (NABU) is investigating criminal proceedings on the fact of misconduct by officials of the Ministry of Ecology when issuing special permits for the use of mineral resources to enterprises founded by Burisma Limited in 2010-2012, that is, the investigation does not cover 2014 when changes in the company's board took place, NABU said.

"The events that NABU's detectives are investigating in this case cover only the period 2010-2012. The changes that took place on the board of Burisma Limited, which have now become the focus of international attention, occurred only in May 2014, therefore they are not and will not be the subject of a probe by NABU," the Bureau said on Facebook on Friday.

In May 2014, U.S. Vice President Joe Biden's son, Hunter Biden, became a member of the Board of Directors at Burisma Limited.