Nazar Kholodnitskiy, the head of the Specialized Anti-Corruption Prosecutor's Office, said in an interview with NV radio that Biden and his son weren't the subject of any investigation.
Hunter Biden served on the board of Ukrainian gas company Burisma at the same time as his father was leading the Obama administration's diplomatic dealings with Kyiv. Though the timing raised concerns among anti-corruption advocates, there has been no evidence of wrongdoing by either the former vice president or his son. Trump also has claimed that Joe Biden pressured the Ukrainian government to shut down a corruption investigation of Burisma, but that claim has been repeatedly discredited.
Kholodnitskiy said in the radio interview that the earlier investigation of Burisma was closed for lack of evidence in 2017, but a court in the Ukrainian capital overruled the move the following year. Despite the court's ruling, the case has remained on hold and the investigation has stalled.
He emphasized that there was no mention of Biden or his son in the Burisma case, which was focused broadly to look into alleged abuse of power by officials in Ukraine's Ministry of Ecology.
Asked if Ukrainian prosecutors could question Biden or his son, Kholodnitskiy said that to do so they would need to see information that would signal possible wrongdoing.
"As of now, there is nothing there," he said. "If it comes up, measures will be taken to check the information."
In the July call, Zelenskiy appears to make an effort to stay in Trump's good graces, telling him at least twice that he is "absolutely right." But after the rough transcript was released by the White House this week, Zelenskiy told reporters he didn't feel pushed, emphasizing that "no one can pressure me." He also sought to play down the situation involving Biden and his son's activities in Ukraine, calling it just one of "many cases that I talk about with leaders of other countries."
The political furor has come as a severe test for Zelenskiy, a comedian without any political experience who was elected in a landslide on promises to uproot the country's endemic corruption and end fighting with Russia-backed separatists in Ukraine's east.
The publication of the call, in which both presidents made critical comments about German Chancellor Angela Merkel and French President Emmanuel Macron, has drawn acerbic comments from Russian officials and lawmakers.
"We are waiting for the party to continue," Russian Foreign Ministry spokeswoman Maria Zakharova said. "Let them publish transcripts of conversations between NATO allies. It would also be useful to publish minutes of closed meetings at the CIA, the FBI and the Pentagon. Put it all on air!"
Zakharova also scoffed at Democratic House Speaker Nancy Pelosi's decision to open an impeachment inquiry based on the call.
"Is it the Democrats' job to make a laughing stock of the United States?" she said. "It's exactly what Ms. Pelosi has done to Congress, the White House and other state institutions."
Asked if Moscow is worried that the White House could similarly publish transcripts of Trump's calls with Russian President Vladimir Putin, Kremlin spokesman Dmitry Peskov said that "we would like to hope that it wouldn't come to that in our relations, which are already troubled by a lot of problems."
Speaking in a conference call with reporters, he emphasized that the publication of the Trump-Zelenskiy call is an internal U.S. issue, but added that it was "quite unusual" to release a confidential call between leaders.
"The materials related to conversations between heads of states are usually classified according to normal international practice," he said.