U.S. Treasury Secretary Steven Mnuchin said on Thursday that he wants to see "very significant" tax reform passed before Congress' August recess and that the Trump administration was looking closely at border tax issues.

"We are committed to tax reforms ... We want to get this done by the August recess," Mnuchin told CNBC, in what was his first interview since taking office last week.

"We've been working closely with the leadership in the House and the Senate and we're looking at a combined plan," he told CNBC. 

Mnuchin said the administration was "primarily focused on a middle income tax cut and a simplification for business," he said.

Most independent analyses have estimated that Trump's tax plan will benefit wealthy people much more than the middle class, CNBC.com reported. In November, Mnuchin told CNBC that he wanted "no absolute tax cut for the upper class," something Sen. Ron Wyden, D-Ore., dubbed the "Mnuchin rule."

President Donald Trump had promised major tax reform and leaner regulations as part of his election campaign, vows that have pushed U.S. equity markets to records highs since the election.

U.S. House Republicans are pushing for a suite of tax changes, including imposing a 20 percent tax on imports, by preventing U.S. companies from deducting import costs from their taxable income to encourage investment and manufacturing in the United States.

Last week the U.S. Senate voted to confirm former Goldman Sachs banker Mnuchin as Treasury Secretary, installing the Trump administration's point-man on tax reform, financial deregulation and economic diplomacy efforts.

Mnuchin stressed that Trump administration tax reform is about helping the middle class, despite widespread concerns that cuts will help the wealthy most.

"Look, as I've said before, we're primarily focused on a middle-income tax cut and simplification for business. And ... on the high end, if there are tax cuts, that they are offset with reduction of deductions and other things," he told CNBC.

"So it's something we're going to carefully look at," he said. "And when we come out with the plan, we'll come obviously out with the distribution and how it impacts people and that's something we're very focused on," he said.