Arlene Foster has said that people should "take her word" that a £435,000 Brexit donation to her party by a little known British-based group was within the electoral rules.
However, the DUP leader refused to name the individuals who made the donation despite repeatedly being asked to do so during an interview with BBC Northern Ireland's The View last night.
"There is nothing to see," said Mrs Foster, who denied that she was being evasive and stated that the Electoral Commission was completely satisfied with her party's actions.
The money was given to the DUP ahead of last year's EU referendum by the Constitutional Research Council (CRC), a British-based group of pro-business figures.
But questions have been raised over the original source of the money.
Part of it was used to buy a four-page supplement in the Metro free-sheet in London and other British cities urging readers to vote Leave.
Mrs Foster said: "We have satisfied ourselves that it kept within all the rules and we are satisfied that it was from UK businessmen.
"So we are quite satisfied with the way it has been handled and so are the Electoral Commission.
"This is a reheated story.
"We dealt with it back at the time of the Assembly election."
The DUP leader said that the story was being promoted by Sinn Fein who were "trying to deflect" from other issues during the Westminster election campaign.
When asked if she knew the identities of the individual donors, Mrs Foster said that she did but she refused to name them. "We are satisfied that the people who gave the donation had every right to give the donation," she said.
"The money came from the CRC, and they got the money from a number of donors who are UK businesspeople.
"As far as I'm concerned, that's the end of the matter."
She insisted that she wasn't concerned that Sinn Fein would be raising the issue with the Electoral Commission at a meeting today.
She added that she had raised her own issues about the behaviour of Sinn Fein polling agents when she met the commission yesterday.
Mrs Foster also said that she had no regrets about describing Sinn Fein's Stormont leader, Michelle O'Neill, as "blonde" in an interview with the Sunday Independent last weekend.
"It was meant as a compliment," Mrs Foster said. "It wasn't a mistake. It was a word association game as you know.
"I think Michelle always presents herself in a very professional way," she added.
Mrs Foster denied that she had shown bad judgment during the interview and stated that she had attempted to be "open with the journalist".
She added: "People know I say it as it is.
"It frustrates me that we are talking about this rather than (other) issues."
When asked about her position on an Irish Language Act, Mrs Foster said that she had "a very useful engagement" with the Irish language community which was ongoing.
"I have yet to be concerned that there is a need for an Irish Language Act but the conversation continues," she said.
The DUP leader explained that the political debate had now widened to include acknowledgement of Ulster-Scots and British culture.