Hunter Biden's attorneys fired back Monday after a private investigation firm again attempted to stage a highly unusual intervention in his ongoing child-custody dispute in Arkansas, this time claiming its investigators have lawfully obtained access to Biden's bank account records and confirmed his involvement in a massive, $156 million "counterfeiting scheme."

In a motion to strike, Biden's legal team unconditionally denied the unverified claims, and called the effort by the Florida-based D&A Investigations another obviously bogus "scheme by a non-party simply to make scandalous allegations in the pending suit to gain media attention without any material or pertinent material."

D&A claimed in its most recent filing Dec. 27 with the court in Independence County, Ark., that it has provided attorneys for Lunden Alexis Roberts, who was seeking custody over the child she said Hunter Biden fathered, "access to [Hunter Biden's] bank account records subject of known felonies including fraud and counterfeiting." D&A was seeking to be added as a party to the case, claiming it could support Roberts' accusations and prove that Biden was involved in illegal activity while dodging discovery quests.

D&A alleged that the "bank account records bear exhibit identifier(s) known by [Hunter Biden] as the subject of criminal investigation(s) both adjudicated and ongoing, of which he is a party to." The firm also claimed the bank records "provide the source and destination bank account numbers of Burisma Holdings Limited, PrivatBank, Bank of China, [Hunter Biden's] business partners, Rosement Seneca Bohai," and others.

Speaking to Fox News late Monday, D&A claimed the FBI and Justice Department have been investigating PrivatBank, the Ukrainian natural gas company Burisma, Biden and others since April 2019 -- and that the investigation remained open. The FBI told Fox News on Tuesday that, as a matter of policy, it does not confirm or deny the existence of ongoing investigations.

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The bank records "verify the counterfeiting scheme accumulating $156,073,944.24 with an average account value (monthly balance) in the amount of $6,785,823.66." Burisma, the filing claimed, financed "Atlantic Council (Ukraine) and associated rogue operatives from the [U.S. State Department], FVEY, and CrowdStrike in Ukraine, suing PrivatBank."

Hunter Biden held a lucrative role on the board of Burisma while his father oversaw Ukraine policy as vice president, prompting even career State Department officials to flag a possible conflict of interest. CrowdStrike is a cybersecurity company that Trump said possessed the Democratic National Committee (DNC) server that was hacked during the 2016 campaign -- a claim that fact-checkers repeatedly have said was wholly invented.

Biden's attorneys did not immediately respond to Fox News' requests for comment late Monday. But, the lawyers told the court that D&A's motion to intervene was riddled with falsehoods and clearly procedurally improper, and that Arkansas law required that intervening parties share some common issue with the existing case.

D&A had not even attempted to explain how its latest filing complied with the law, Biden's team said, noting that the latest motion to intervene simply outlined a series of accusations with no legal or factual support.

The court has not yet ruled on Biden's latest motion to strike. Shortly after Biden's team filed, an individual in Jerusalem, Joel Caplan, submitted his own bizarre motion to intervene, saying he has lost money in the "China hustle." Caplan, representing himself, wrote that his investments were "basically robbed" overseas -- then ended his motion by telling the court, "Thank you for your time!"

D&A was the same firm that worked with the defense team of Casey Anthony, a Florida woman acquitted of murdering her child in a highly publicized trial in 2011. Anthony later accused the private investigator of smearing her for media attention.

And, D&A's website is full of head-turning and unsubstantiated claims, including that CNN anchor Jake Tapper was a "propaganda actor" for Netflix. The website also called Democrats' impeachment efforts against Trump a "sham."

The legal saga began last week. D&A asserted in a Dec. 23 "Notice of Fraud and Counterfeiting and Production of Evidence" filed with the Arkansas court that the 49-year-old Biden was the subject of multiple criminal probes and "established bank and financial accounts with Morgan Stanley et al" for Burisma for a "money laundering scheme."

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The court quickly struck that filing, saying it had violated state procedural rules which required that intervening parties raise a claim that shared a "question of law or fact in common" with the existing case.

Then, the firm told Fox News to expect another filing soon -- and asserted its investigators have found that the intelligence community whistleblower at the center of the Democrats' impeachment of President Trump accompanied Joe Biden when he traveled to Ukraine in early 2016 and, by his own admission, pressured the country's government to fire its top prosecutor by threatening to withhold $1 billion in U.S. aid.

The whistleblower's attorney, Mark Zaid, did not respond to Fox News' request for comment on D&A's claims, which Fox News has not independently verified. Zaid previously has acknowledged that the whistleblower had "contact" with presidential candidates of both parties, amid reports that he had a "professional working relationship" with one of the Democrats seeking the White House in 2020.

Zaid openly declared that a "coup has started" against the administration all the way back in 2017, and promised that impeachment would result.

D&A's incendiary claims highlighted some unanswered questions that could arise in a possible GOP-led impeachment trial in the Senate. Most notably, after leaving the vice presidency, Joe Biden attended a conference at which he discussed a previously unreported meeting in Ukraine for the first time.

"I said, 'I’m telling you, you’re not getting the billion dollars,'" Biden boasted at the conference. "I said, 'You’re not getting the billion. I’m going to be leaving here in --,' I think it was about six hours. 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 b----. He got fired, and they put in place someone who was solid at the time."

The prosecutor, Viktor Shokin, was fired in March 2016, and had widely been accused of corruption himself. However, publicly available records showed that Joe Biden did not officially travel to Ukraine in 2016.

Meanwhile, in her filing in the case, the 28-year-old Roberts claimed Hunter Biden has "had no involvement in the child's life since the child's birth, never interacted with the child, never parented the child," and "could not identify the child out of a photo lineup."

READ LUNDEN ROBERTS' MOTION FOR CUSTODY, SAYING BIDEN HAS BEEN AN ABSENT FATHER

DNA tests allegedly confirmed "with scientific certainty" that Hunter Biden was the biological father of Roberts' baby, according to court documents filed in November.

Joe Biden tangled with a Fox News reporter when asked about that development.

"I'm wondering if you have a comment on this report, and court filing, out of Arkansas, that your son Hunter just made you a grandfather again," Fox News’ Peter Doocy asked.

"No, that’s a private matter and I have no comment," Biden fired back before attacking the reporter.

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"Only you would ask that," Biden said. "You're a good man. You're a good man. Classy."

Hunter Biden reportedly is expecting a child with his wife Melissa Cohen Biden, whom he married this past May.

Fox News' Brian Flood contributed to this report.