KIEV, Ukraine — Ukraine’s top prosecutor said on Friday he would audit several important cases previously handled by his predecessors, including a criminal case involving the owner of a natural gas company that employed a son of former Vice President Joseph R. Biden Jr.
The development came amid an impeachment inquiry against President Trump connected to a request he made to the Ukrainian president during a July phone call asking him to investigate Mr. Biden, a Democratic presidential candidate, and his son’s work in Ukraine.
The prosecutor’s announcement raised questions about whether Ukraine was bowing to public and private pressure from the president of the United States, on which it has depended on for millions of dollars in aid. But it did not — by design, analysts of Kiev’s tactics in the crisis say — answer those questions.
As pressure from allies of Mr. Trump mounted over the summer to start the investigation, Ukraine’s president and aides avoided any public commitment to doing so, kicking down the road any move that would signal taking sides in American politics.
The audit, which the general prosecutor’s office said in a statement must be completed before any decision is taken on an actual investigation, could stretch on for months, or even until the end of the American presidential election next year, analysts said.
“This could go on for a long time,” said Volodymyr Fesenko, the director of the Penta analytical center. “I don’t think the prosecutor is going to be rushing with this. It’s better not to hurry.”
Mr. Ryaboshapka said at a news conference in Kiev on Friday that the name of Mr. Biden “may be” in the cases now under review. In deciding to initiate the audit, he said, “the key words were not Biden and not Burisma.”
“The key was those proceedings which were closed or investigated by the previous leadership,” Mr. Ryaboshapka explained, but allowed, “In this large number of cases, there may be ones with these two words.”
a leading contender in next year’s presidential election. They have tried to signal to Mr. Trump and his allies that the issues will be investigated, even as they tried to telegraph to Democrats that they were not bending to Mr. Trump’s pressure.
At the same time, the prosecutor’s announcement signaled some attention to an issue Mr. Trump raised in the phone call in July and had repeated publicly: a Ukrainian government investigation of a case touching on a likely opponent in next year’s election.
Mr. Trump’s July phone call with President Volodymyr Zelensky of Ukraine is central to the formal House committee impeachment inquiry called by Speaker Nancy Pelosi. The inquiry is examining whether Mr. Trump betrayed his oath of office and the nation’s security by seeking to enlist the aid of a foreign power to tarnish a political rival.
On the call, Mr. Zelensky suggested that he would assist with an investigation of Burisma, according to White House notes of the call. The Ukrainian president said that a new prosecutor general would soon be appointed who would be “100 percent my person” and would “look into the situation.”
The Ukrainian president said his country was also almost ready to purchase anti-tank missiles, made by Raytheon, to be used to better repel armored assaults by Russian-supported fighters. Mr. Trump responded, “I’d like you to do us a favor, though.”
Mr. Trump has vigorously denied doing anything wrong, and allies of the president said that a reconstructed transcript of the call showed no quid pro quo, making the impeachment inquiry baseless. But Democrats said that Mr. Trump’s request for a favor, and the fact that he had already withheld millions in aid from Ukraine before the call, raised serious questions that must be examined.
On Thursday, the State Department gave initial approval to the $39.2 million sale of 150 Javelin missiles and related equipment to Ukraine. The sale of the javelins to Ukraine must still go through Congress. Ukraine has been fighting Russia for five years in eastern Ukraine since Moscow’s seizure of Crimea.
At the news briefing, Mr. Ryaboshapka said he had not received any phone calls about the cases or come under undue pressure on other matters. “No foreign or domestic politicians, officials or people who are not officials called me and tried to influence my decisions on specific criminal proceedings,” he said.
Mr. Ryaboshapka added: “The prosecution service is beyond politics. We are conducting an audit of all cases, including those which were investigated by the previous leadership of the prosecutor’s office.”
If laws were violated, he added, “we will react accordingly.” Asked whether he had any evidence of wrongdoing by Hunter Biden, he told reporters, “I have no such information.”
No evidence of wrongdoing by Mr. Biden or his son has emerged, and the elder Mr. Biden has denied the accusations. But Mr. Trump has doubled down, urging China to investigate the Bidens and charging that the country lavished $1.5 billion on Hunter Biden in order to influence his father and win favorable trade deals with the United States.
Zlata Symonenko, a legal analyst with Reanimation Package of Reforms, a group advising the government on legislation, said prosecutorial audits typically require about three months for each case. The prosecutor’s office said the audit would review 15 cases “successively,” potentially putting off any decision on the Biden-related material for more than three years — well after next year’s presidential election in the United States.
Mr. Ryaboshapka’s comments on Friday were the first indication of how Ukrainian criminal justice officials will handle one of the matters that Mr. Trump raised in the call. Mr. Trump also asked Mr. Zelensky to look into whether Ukrainians had framed Russia for hacking the 2016 presidential election — an idea his own former Homeland Security secretary, Thomas P. Bossert, called “totally debunked.”
It’s not clear what, if anything, Ukrainians have done in response to that request.