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The National Anti-corruption Bureau of Ukraine (NABU) says its detectives are probing into Burisma Holdings Limited's activity over possible abuse of office by Ecology Ministry officials before U.S. Vice President Joe Biden's son, Hunter Biden, joined the company's supervisory board.

"NABU is investigating criminal proceedings on the fact of misconduct by officials of the Ecology Ministry during [Viktor] Yanukovych's presidency when special mineral resources permits were issued to a number of enterprises whose founder is Burisma Limited with the ex-minister of ecology being the ultimate beneficiary," NABU said on Facebook on September 27.

In particular, the events that NABU detectives are investigating in this case cover only the period of 2010-2012, it said.

Read alsoEx-prosecutor general Lutsenko says Biden's son did not violate Ukraine's laws

"The changes that occurred in Burisma Limited's board [Biden's son became one of the members of the Burisma supervisory board in 2014], which have now become the focus of attention of the international community, took place in May 2014, therefore they are not and have never been the subject of NABU investigations," the Bureau emphasized.

"Checking the activities of board members of private business entities in the periods that are not related to the period covered by the possible crime is not within NABU's jurisdiction," the Bureau said.

UNIAN memo. Ukrainian authorities have been probing into money laundering in the amount of over US$33 million during the acquisition of a group of companies of Kherson oil transshipment, in which Wirelogic Technology AS, Digitex Organization LLP, and ex-Minister of Ecology, businessman Mykola Zlochevsky's Burisma Holdings Limited were involved. Hunter Biden, son of former U.S. Vice President Joe Biden, was a member of the latter's board.

On May 14, the then Prosecutor General, Yuriy Lutsenko, said that Ukraine was ready to transfer materials on Burisma to U.S. law enforcement agencies. According to him, the investigation had a printout of all Burisma payments, including to senior U.S. officials. Yet, Lutsenko emphasized, the foreigners who were involved in the management of Burisma had not violated Ukrainian legislation.

On September 24, after a whistleblower's complaint, the White House unprecedentedly published a redacted version of the memorandum of the July 25 telephone conversation between U.S. President Donald Trump and his Ukrainian counterpart Volodymyr Zelensky, which became the cause behind a formal impeachment inquiry into Trump.

According to the memorandum, Trump repeatedly asked Zelensky to "look into" the situation regarding a probe into former U.S. Vice President Joe Biden's son in Ukraine.