US Republican presidential candidate Donald Trump has pushed back against renewed calls for him to release his tax returns before the election, saying the rate that he pays is "none of your business."
Mr Trump, who has all but locked up the Republican Party's nomination for the November 8 presidential election, has said the Internal Revenue Service is auditing his returns and he wants to wait until the review is over before making them public.
"It should be, and I hope it's before the election," Mr Trump told ABC's Good Morning America on Friday (local time).
Mr Trump is building out his policy proposals as he pivots to the general election, including tapping experts in various fields.
Among those he has asked for help is US Republican Representative Kevin Cramer of North Dakota, one of the country's most ardent oil and gas drilling advocates and climate change sceptics.
North Dakota has been at the forefront of the US shale oil and gas boom. Cramer endorsed Mr Trump earlier this year.
Mr Trump has asked Cramer to write a white paper on energy policy, Cramer and sources familiar with the matter told Reuters. A white paper is a detailed report on a topic.
But the ins and outs of campaigning continue to be a major topic with Mr Trump, who has never held elected office.
On Friday, the billionaire real estate developer, who has often boasted of his wealth, was asked why he had been willing in the past to release his tax information to Pennsylvania and New Jersey officials when seeking casino licences, even though he was being audited by the Internal Revenue Service.
"At the time it didn't make any difference to me. Now it does," Mr Trump said.
Pressed on what tax rate he pays, Mr Trump refused to say.
"It's none of your business," he said.
"Before 1976, people didn't do it. It used to be a secret thing," he added.
Mr Trump said his company was "clean."
"I don't have Swiss bank accounts, I don't have offshore accounts," he said.
The 2012 Republican presidential nominee, former Massachusetts Governor Mitt Romney, has been scathing in his criticism of Mr Trump and said this week it was "disqualifying" for a nominee to refuse to make his tax returns public.
"There is only one logical explanation for Mr Trump's refusal to release his returns: There is a bombshell in them," Romney said in a Facebook post on Wednesday.