Kiev, Ukraine (CNN) Former Ukrainian President Petro Poroshenko has told CNN that he had no knowledge about his prosecutor-general's offer to help US President Donald Trump investigate the son of former Vice President Joe Biden , a leading candidate to face him in the 2020 presidential election.

In a brief exchange in the capital Kiev on Wednesday, Poroshenko said he had no information and did not send one of his general prosecutors, Yuriy Lutsenko , to meet with Trump's personal attorney Rudy Giuliani.

Giuliani says he twice met with Lutsenko -- in New York in January 2019, then in Warsaw in February.

Giuliani previously told CNN that Lutsenko, who was prosecutor under Poroshenko and his successor Volodymyr Zelensky until August, shared information with him related to allegations that Biden thwarted an investigation into his son Hunter's business dealings with a Ukrainian natural gas company, Burisma. There has been no evidence of wrongdoing on the part of Biden or his son.

In an April interview with the Babel, a Ukrainian news outlet, Lutsenko confirmed Giuliani's account of their conversations.

The alleged investigation into Burisma and Biden was central to a July phone call in which Trump repeatedly asked Zelensky to look into the Biden family, while simultaneously withholding almost $400 million worth of military aid to Ukraine. Trump has denied his decision to delay the aid had anything to do with his desire for Ukraine to investigate Biden.

whistleblower complaint about that call has prompted an impeachment inquiry, focused on Trump and Giuliani's Ukraine dealings.

Asked whether he sent Lutsenko to meet Giuliani, Poroshenko said: "I knew nothing about it."

The former mayor of New York City has also repeatedly pushed a theory that the origins of the investigation into Russian interference in the 2016 election can be traced back to Democrats' dealings in Ukraine. Giuliani told CNN he learned more about the Russian interference, as well as the Biden allegations, from Lutsenko.

But Lutsenko, whose hold on power was precarious following Ukraine's April presidential election, ultimately backed off some of his claims that Giuliani worked to amplify, including that his office was reopening its investigation into Burisma and Biden.

According to the whistleblower's complaint, Giuliani's interactions with Ukrainian officials prompted concern among US officials about the "circumvention of national security decision-making processes."

Giuliani told CNN he never heard about any of those concerns. "If they were going to get upset about this, they should have gotten upset about it in January or February," he said.

On Wednesday, Poroshenko also denied ever speaking to Biden about his son's business interests in Ukraine. Nor, Poroshenko said, did he speak to former US President Barack Obama or Trump about any commercial or personal business dealings.

"We never, ever spoke about commercial activity but we spoke about the form of the prosecutor general office, created condition for the independence of that," Poroshenko said. "And now, unfortunately, by the law adopted now by parliament, the independence of the prosecutor's office was completely ruined."

Asked whether he had fired former Ukrainian prosecutor general Viktor Shokin -- Lutsenko's predecessor -- because "he was investigating Burisma and Biden," Poroshenko said he did not want to get involved in US politics and said that all general prosecutors in his country should be completely independent.

Trump has repeatedly claimed Shokin was investigating Hunter Biden. For example, Trump alleged on September 21 that the media wanted to avoid talking about the "Joe Biden demand that the Ukrainian Government fire a prosecutor who was investigating his son..."

But there is no evidence that Hunter Biden was himself ever under investigation.