Treasury Secretary Steven Mnuchin said Sunday the Trump administration isn't considering a tax increase on wealthier Americans, knocking down a report that White House adviser Steve Bannon had floated the idea as a way to pay for tax cuts for middle-income taxpayers.

"I have never heard Steve mention that," Mnuchin said.

The administration is aiming to release its full tax plan by September and have Congress approve it by the end of the year, Mnuchin said on ABC News' "This Week." So far, the administration has issued a one-page summary of broad principles for tax reform, but few details.

The administration says it wants to reduce the top income tax bracket from 39.6 percent to 35 percent and lower tax rates for the middle class. Bannon's idea would boost the top rate above 40 percent for people who earn nearly $420,000 a year or more, according to a July 2 report on the website Axios.

The GOP congressional leadership and the Trump administration have struggled with the issue of how to offset the cost of tax cuts.

Mnuchin said the administration's plan would pay for itself, but that's only if about $2 trillion in increased revenue resulting from projected faster economic growth is included. Yet congressional budget scorekeepers may not agree that tax cuts would produce such growth.

Under congressional budget rules, tax cuts can be passed with a simple majority in the U.S. Senate, but only if they don't increase the deficit after 10 years. That would allow Republicans, who have 52 Senate seats, to pass the bill without any Democratic votes.