Ukrainian investigators have begun an inquiry into then-Vice President Joe Biden over allegations that he pressured officials into firing a top prosecutor in 2016.

A case revolving around Biden, now a Democratic candidate for president, was opened by the State Bureau of Investigations on a court order following a January appeal for action by Viktor Shokin, the dismissed prosecutor general's lawyer, Oleksandr Teleshetsky, told the Washington Post.

“They need to investigate this. They have no other alternative. They are required to do this by the decision of the court. If they don't, then they violate a whole string of procedural norms,” Teleshetsky said.

The State Bureau of Investigations confirmed an inquiry was opened. The case mentions only a U.S. citizen and does not refer to Biden by name.

Daria Kaleniuk, director of Ukraine’s Anti-Corruption Action Center, downplayed the significance of the matter, saying that Ukrainian law requires state investigators to open a case on a court order even if they don't believe there is enough evidence. “If I was a SBI investigator, I would close that case immediately,” she said.

Shokin, who was dismissed in March 2016 after about a year in office by then-President Petro Poroshenko, claims he was ousted because he wanted to investigate the lucrative role Hunter Biden, the son of Joe Biden, had on the board of Ukrainian energy company Burisma Holdings. President Trump, his personal lawyer Rudy Giuliani, and other allies also claim Biden improperly used his position as vice president to pressure Ukraine to fire Shokin to protect his son from an investigation into Burisma.

The elder Biden threatened to withhold $1 billion in U.S. loan guarantees if Ukraine did not fire its top prosecutor, who was criticized by the West for not doing enough to crack down on corruption. The European Union, the International Monetary Fund, and other allies had the same objective, and Biden was repeating U.S. policy that had been set out by Washington’s ambassador to Kyiv in the preceding months and was briefed by White House staff just ahead of the trip.

Biden says there is no "credibility" to the claims of corruption, but his critics have seized on video of a statement the former vice president made in January 2018, where he boasted to members of a panel hosted by the Council of Foreign Relations that he ordered the Ukrainian government to fire Shokin or the White House would renege on a commitment to provide aid. “I looked at them and said: ‘I’m leaving in six hours. If the prosecutor is not fired, you’re not getting the money.’ Well, son of a bitch. He got fired," Biden said.

The matter got wrapped up into the impeachment saga after Trump pressed Ukrainian President Volodymyr Zelensky to investigate the Bidens and other Democrats in a July 25 phone call in which he also appeared to praise Shokin and call his removal "unfair," according to a transcript released by the White House. Democrats cried foul over what they interpreted to be a "quid pro quo."

At issue was whether the president improperly pressured Ukraine to announce investigations by withholding military aid and dangling the possibility of a White House meeting between the Trump and Zelensky. Trump was impeached by the Democratic-controlled House on charges of abuse of power and obstruction of Congress, but he was acquitted by the GOP-led Senate earlier this month. Zelensky himself has repeatedly stated that he felt no pressure from Trump to open an investigation into the Bidens.

Earlier this month, Zelensky fired his chief of staff and replaced him with Andriy Yermak, an aide who met with Giuliani, who also met with Shokin as far back as late 2018 as he sought political dirt on the Bidens.