Susan Collins, the US senator of Maine, has dismissed allegations that she traded federal contracts for campaign cash as “completely false” after it emerged the FBI examined the claims.

Asked by a reporter about an ethics complaint filed last week by a Maine attorney, the Republican – currently campaigning to retain her seat ahead of November’s US midterm elections – said the allegations were recycled from 2020 and had been rejected by the Department of Justice, the FBI and the Federal Election Commission.

“The allegations are completely false,” Collins said. She said the University of Maine, not the defense contractor Navatek, had asked her to back a research grant, and that she had never heard of the company. Its former chief executive, Martin Kao, she said, was “a crook” whom neither she, nor the university, knew about.

“We have a picture of his meeting with me and with other people in my office that is many months before he ever made a single contribution,” she added. “He spun this story up again in the hopes that the judge would be lenient, or the prosecutor would be.”

ProPublica reported in September that Kao, Navatek’s former president and CEO, told FBI agents and prosecutors that his company won millions in federal funding by bankrolling politicians, with Collins his most important patron. Kao, who is serving 87 months for fraud and campaign finance crimes, claimed the head of Collins’s Super Pac asked him for $500,000 in 2019. He claimed he then sent $150,000 through a shell company, and that Collins’s office later promised to secure $32m in naval contracts. ProPublica reported that the Senate allocated at least $10m that year based on Navatek’s proposals, funding Collins says she backed only because the University of Maine asked her to, but did not report that the full $32m was awarded.

The outlet said it reviewed a trove of FBI evidence and thousands of pages of legal records, and interviewed dozens of people familiar with Navatek and the inquiry, and independently corroborated much of Kao’s account. Among the emails it cited was one in which the Super Pac chair, Scott Reed, replied “Very smart” to Kao’s shell company plan, and another asking for Kao’s phone number so Collins could thank him.

ProPublica also reported that FBI agents sought to open a broader bribery investigation in 2024, which collapsed after Donald Trump returned to office and purged the bureau’s public corruption teams.

No one in Collins’s orbit was charged. Kao declined to be interviewed, and Reed denied discussing Kao or Navatek with Collins or her staff.

Pressed on why she would not welcome an ethics inquiry to clear her name, Collins said it was not up to her, and dismissed the complaint as the work of “partisan Democrats” and Valerie Adams, a lawyer in Maine “who lost her election” in the June primary to be district attorney.

“I was never even interviewed because there was no evidence for it,” Collins said.