An FBI informant has been charged with lying to his handler about ties between Joe Biden, his son Hunter and a Ukrainian energy company. Alexander Smirnov falsely told FBI agents in June 2020 that executives associated with the Ukrainian energy company Burisma paid Hunter and Joe Biden $5m each in 2015 and 2016, prosecutors said on Thursday. Smirnov told the FBI that a Burisma executive had claimed to have hired Hunter Biden to “protect us, through his dad, from all kinds of problems”, prosecutors said in a statement. The allegations became a flashpoint in Congress over the summer as Republicans demanded the FBI release the unredacted form documenting the allegations as they pursued investigations of Biden and his family. They acknowledged at the time that it was unclear if the allegations were true. The new development sharply undermines the thrust of congressional Republicans’ corruption accusations that the US president was making money from his son Hunter’s business dealings in Ukraine. Smirnov, 43, appeared in court in Las Vegas briefly on Thursday after being charged with making a false statement and creating a false and fictitious record. He did not enter a plea. The judge ordered the courtroom cleared after federal public defender Margaret Wightman Lambrose requested a closed hearing for arguments about sealing court documents. She declined to comment on the case. The charges were filed by the justice department special counsel David Weiss, who has separately charged Hunter with firearm and tax violations. Hunter’s legal team did not immediately return a message seeking comment. The informant’s claims have been central to the Republican effort in Congress to investigate the president and his family, and helped spark what is now a House impeachment inquiry into Biden. Prosecutors say Smirnov had contact with Burisma executives, but it was routine and actually took place in 2017, after Barack Obama, the US president, and Biden, his vice-president, had left office – when Biden would have had no ability to influence US policy. Smirnov “transformed his routine and unextraordinary business contacts with Burisma in 2017 and later into bribery allegations against public official 1, the presumptive nominee of one of the two major political parties for president, after expressing bias against public official 1 and his candidacy,” the indictment said. He repeated some of the false claims when he was interviewed by FBI agents in September last year and changed his story about others and “promoted a new false narrative after he said he met with Russian officials”, prosecutors said. If convicted, Smirnov faces a maximum penalty of 25 years in prison. The House oversight committee chairman James Comer, a Republican representing Kentucky, had subpoenaed the FBI last year for the so-called FD-1023 document as Republicans deepened their inquiries into the US president and Hunter ahead of the 2024 presidential election. Working alongside Comer, the Republican senator Chuck Grassley of Iowa released an unclassified document that Republicans at the time claimed was significant in their investigation of Hunter. It added to information that had been widely aired during Donald Trump’s first impeachment trial involving Trump attorney Rudy Giuliani’s efforts to dig up dirt on the Bidens ahead of the 2020 election. The White House said at the time that the claims had been debunked for years. The impeachment inquiry into Biden over his son’s business dealings has lagged in the House, but the panel is pushing ahead with its work. Hunter is expected to appear before the committee later this month for an interview.